diff --git a/.changeset/zero-rust-define.md b/.changeset/zero-rust-define.md
new file mode 100644
index 0000000000..6d050a3eee
--- /dev/null
+++ b/.changeset/zero-rust-define.md
@@ -0,0 +1,5 @@
+---
+'zero-rust': minor
+---
+
+Add typed named queries and mutators behind a new `serde` feature, shaped like the Swift client's `defineQuery` and `defineMutator`. `define::define_query(name, |args, ctx| query)` and `define::define_mutator(name, |tx, args, ctx| ...)` take serde argument types, and `.with(args)` makes a `QueryRequest` for `materialize`, `run`, and `preload` (built with the `Zero`'s context) or a `client::MutateRequest` for the new `Zero::mutate_request`. `json::Value` implements serde, with `json::to_value` and `json::from_value`. `materialize`, `run`, and `preload` now take any `query::ZeroQuery` (an `AnyQuery`, a typed `Query`, or a `QueryRequest`), so existing calls keep working; the default build still has no third-party dependencies.
diff --git a/apps/zbugs-gpui/Cargo.lock b/apps/zbugs-gpui/Cargo.lock
index a10be6bfff..2f9008a416 100644
--- a/apps/zbugs-gpui/Cargo.lock
+++ b/apps/zbugs-gpui/Cargo.lock
@@ -8399,7 +8399,6 @@ version = "0.0.0"
 dependencies = [
  "getrandom 0.4.3",
  "serde",
- "serde_json",
  "zero-client",
 ]
 
@@ -8592,6 +8591,7 @@ name = "zero-client"
 version = "0.1.3"
 dependencies = [
  "rusqlite",
+ "serde",
 ]
 
 [[package]]
diff --git a/apps/zbugs-gpui/Cargo.toml b/apps/zbugs-gpui/Cargo.toml
index 4db0a4016d..ac83f1f9c5 100644
--- a/apps/zbugs-gpui/Cargo.toml
+++ b/apps/zbugs-gpui/Cargo.toml
@@ -43,7 +43,10 @@ tokio-tungstenite = { version = "0.30", default-features = false, features = [
 ureq = { version = "3", default-features = false, features = ["rustls"] }
 zbugs-model = { path = "../zbugs-model" }
 # SQLite storage, so the app keeps its data across launches.
-zero-client = { path = "../../rust/zero-client", features = ["sqlite"] }
+zero-client = { path = "../../rust/zero-client", features = [
+  "sqlite",
+  "serde",
+] }
 
 [features]
 # The end-to-end run CI does against zbugs' backend: see src/app/e2e.rs.
diff --git a/apps/zbugs-gpui/src/app.rs b/apps/zbugs-gpui/src/app.rs
index a0b737988c..aeed8672b6 100644
--- a/apps/zbugs-gpui/src/app.rs
+++ b/apps/zbugs-gpui/src/app.rs
@@ -31,8 +31,8 @@ use std::rc::Rc;
 use zbugs_model::args::*;
 use zbugs_model::mutators::{
     ADD_COMMENT, ADD_EMOJI_TO_COMMENT, ADD_EMOJI_TO_ISSUE, ADD_LABEL, CREATE_AND_ADD_LABEL,
-    CREATE_ISSUE, DELETE_ISSUE, DELETE_ISSUES, EDIT_COMMENT, MutateRequest, REMOVE_COMMENT,
-    REMOVE_EMOJI, REMOVE_LABEL, SET_USER_PREF, SET_VIEW_STATE, UPDATE_ISSUE, UPDATE_NOTIFICATION,
+    CREATE_ISSUE, DELETE_ISSUE, DELETE_ISSUES, EDIT_COMMENT, REMOVE_COMMENT, REMOVE_EMOJI,
+    REMOVE_LABEL, SET_USER_PREF, SET_VIEW_STATE, UPDATE_ISSUE, UPDATE_NOTIFICATION,
 };
 use zbugs_model::queries::{
     ALL_PROJECTS, COMMENTS_PAGE, ISSUE_DETAIL, ISSUE_LIST_COUNT, ISSUE_LIST_V2, LABELS, USER,
@@ -40,7 +40,7 @@ use zbugs_model::queries::{
 };
 use zbugs_model::schema::{Comment, Emoji, Issue, IssueVisibility, Label, Project, User, UserPref};
 use zbugs_model::{AuthData, ZERO_PROJECT_NAME, make_id};
-use zero_client::client::{ConnectionState, MutationOutcome};
+use zero_client::client::{ConnectionState, MutateRequest, MutationOutcome};
 use zero_client::ttl::Ttl;
 
 /// Rows the list asks for at a time, as zbugs' list pages.
@@ -468,16 +468,15 @@ impl ZbugsApp {
         });
 
         let (list, count) = Self::queries(&session, &filters, limit, cx);
-        let auth = session.auth.as_ref();
-        let projects = Live::new(&session.zero, ALL_PROJECTS.call(&(), auth), &ttl(), cx);
+        let projects = Live::new(&session.zero, ALL_PROJECTS.with(()), &ttl(), cx);
         let (creators, assignees, crew, labels) =
             Self::project_lives(&session, &filters.project, cx);
         let me = session
             .auth
             .as_ref()
-            .map(|a| Live::new(&session.zero, USER.call(&a.sub, Some(a)), &ttl(), cx));
-        let skin_tone = session.auth.as_ref().map(|a| {
-            let q = USER_PREF.call(&SKIN_TONE_PREF.to_owned(), Some(a));
+            .map(|a| Live::new(&session.zero, USER.with(a.sub.clone()), &ttl(), cx));
+        let skin_tone = session.auth.as_ref().map(|_| {
+            let q = USER_PREF.with(SKIN_TONE_PREF.to_owned());
             Live::new(&session.zero, q, &ttl(), cx)
         });
         // A zero-cache address the client can't take, from the environment
@@ -746,7 +745,7 @@ impl ZbugsApp {
             label_name: name,
             project_id: None,
         };
-        self.mutate(CREATE_AND_ADD_LABEL.with(&args), cx);
+        self.mutate(CREATE_AND_ADD_LABEL.with(args), cx);
         true
     }
 
@@ -883,7 +882,6 @@ impl ZbugsApp {
 
     /// The creators, assignees, crew, and labels of `project`.
     fn project_lives(session: &Session, project: &str, cx: &mut Context<Self>) -> ProjectLives {
-        let auth = session.auth.as_ref();
         let mut users = |filter| {
             let args = UsersForProjectArgs {
                 disabled: false,
@@ -891,12 +889,7 @@ impl ZbugsApp {
                 project_name: project.into(),
                 filter: Some(filter),
             };
-            Live::new(
-                &session.zero,
-                USERS_FOR_PROJECT.call(&args, auth),
-                &ttl(),
-                cx,
-            )
+            Live::new(&session.zero, USERS_FOR_PROJECT.with(args), &ttl(), cx)
         };
         let creators = users(UsersFilter::Creators);
         let assignees = users(UsersFilter::Assignees);
@@ -904,7 +897,7 @@ impl ZbugsApp {
         let args = ProjectArgs {
             project_name: project.into(),
         };
-        let labels = Live::new(&session.zero, LABELS.call(&args, auth), &ttl(), cx);
+        let labels = Live::new(&session.zero, LABELS.with(args), &ttl(), cx);
         (creators, assignees, crew, labels)
     }
 
@@ -962,19 +955,15 @@ impl ZbugsApp {
         limit: i64,
         cx: &mut Context<Self>,
     ) -> (Live<Vec<Issue>>, Live<i64>) {
-        let auth = session.auth.as_ref();
         let list_context = Self::list_context(filters);
-        let list = ISSUE_LIST_V2.call(
-            &IssueListV2Args {
-                list_context: list_context.clone(),
-                limit: Some(limit),
-                start: None,
-                dir: PageDirection::Forward,
-                inclusive: None,
-            },
-            auth,
-        );
-        let count = ISSUE_LIST_COUNT.call(&IssueListCountArgs { list_context }, auth);
+        let list = ISSUE_LIST_V2.with(IssueListV2Args {
+            list_context: list_context.clone(),
+            limit: Some(limit),
+            start: None,
+            dir: PageDirection::Forward,
+            inclusive: None,
+        });
+        let count = ISSUE_LIST_COUNT.with(IssueListCountArgs { list_context });
         (
             Live::new(&session.zero, list, &ttl(), cx),
             Live::new(&session.zero, count, &ttl(), cx),
@@ -1034,13 +1023,10 @@ impl ZbugsApp {
         if self.selected.as_deref() == Some(id.as_str()) {
             return;
         }
-        let q = ISSUE_DETAIL.call(
-            &IssueDetailArgs {
-                id_field: IdField::Id,
-                id: IssueKey::String(id.clone()),
-            },
-            self.session.auth.as_ref(),
-        );
+        let q = ISSUE_DETAIL.with(IssueDetailArgs {
+            id_field: IdField::Id,
+            id: IssueKey::String(id.clone()),
+        });
         self.detail = Some(Live::new(&self.session.zero, q, &ttl(), cx));
         self.selected = Some(id);
         self.comments_limit = COMMENT_PAGE;
@@ -1105,7 +1091,7 @@ impl ZbugsApp {
             dir: PageDirection::Backward,
             inclusive: false,
         };
-        let q = COMMENTS_PAGE.call(&args, self.session.auth.as_ref());
+        let q = COMMENTS_PAGE.with(args);
         self.comment_page = Some(Live::new(&self.session.zero, q, &ttl(), cx));
         cx.notify();
     }
@@ -1113,7 +1099,7 @@ impl ZbugsApp {
     /// Runs a mutation and shows why it failed, on the client or the
     /// server.
     fn mutate(&mut self, request: MutateRequest, cx: &mut Context<Self>) {
-        let result = request.run(&self.session.zero);
+        let result = self.session.zero.mutate_request(request);
         if let Some(Ok(MutationOutcome::AppError { message, .. })) = result.client.result() {
             self.error = Some(message);
             cx.notify();
@@ -1203,12 +1189,12 @@ impl ZbugsApp {
             cx.notify();
             return false;
         }
-        self.mutate(EDIT_COMMENT.with(&EditCommentArgs { id, body }), cx);
+        self.mutate(EDIT_COMMENT.with(EditCommentArgs { id, body }), cx);
         true
     }
 
     fn delete_comment(&mut self, id: &String, cx: &mut Context<Self>) {
-        self.mutate(REMOVE_COMMENT.with(id), cx);
+        self.mutate(REMOVE_COMMENT.with(id.to_owned()), cx);
     }
 
     /// Asks before a delete, which `delete` does.
@@ -1252,7 +1238,7 @@ impl ZbugsApp {
     /// Deletes issue `id`, and leaves it if it's selected, as the web app
     /// goes back to the list.
     fn delete_issue(&mut self, id: &String, cx: &mut Context<Self>) {
-        self.mutate(DELETE_ISSUE.with(id), cx);
+        self.mutate(DELETE_ISSUE.with(id.to_owned()), cx);
         self.leave_deleted(std::slice::from_ref(id), cx);
     }
 
@@ -1296,7 +1282,7 @@ impl ZbugsApp {
             return;
         };
         let ids = checked.into_iter().collect::<Vec<_>>();
-        self.mutate(DELETE_ISSUES.with(&ids), cx);
+        self.mutate(DELETE_ISSUES.with(ids.clone()), cx);
         self.leave_deleted(&ids, cx);
     }
 
@@ -1322,7 +1308,7 @@ impl ZbugsApp {
             }),
             ..UpdateIssueArgs::new(issue_id, now_ms())
         };
-        self.mutate(UPDATE_ISSUE.with(&args), cx);
+        self.mutate(UPDATE_ISSUE.with(args), cx);
     }
 
     fn set_subscribed(&mut self, issue_id: String, subscribe: bool, cx: &mut Context<Self>) {
@@ -1335,7 +1321,7 @@ impl ZbugsApp {
             },
             created: now_ms(),
         };
-        self.mutate(UPDATE_NOTIFICATION.with(&args), cx);
+        self.mutate(UPDATE_NOTIFICATION.with(args), cx);
     }
 
     /// Tells the user when someone else comments on or reacts to the
@@ -1466,7 +1452,7 @@ impl ZbugsApp {
                         issue_id: id,
                         viewed: now_ms().max(modified),
                     };
-                    this.mutate(SET_VIEW_STATE.with(&args), cx);
+                    this.mutate(SET_VIEW_STATE.with(args), cx);
                 }
                 this.mark_viewed(cx);
             });
@@ -1479,7 +1465,7 @@ impl ZbugsApp {
             open: Some(!issue.open),
             ..UpdateIssueArgs::new(issue.id.clone(), now_ms())
         };
-        self.mutate(UPDATE_ISSUE.with(&args), cx);
+        self.mutate(UPDATE_ISSUE.with(args), cx);
     }
 
     fn set_assignee(&mut self, issue_id: String, user_id: Option<String>, cx: &mut Context<Self>) {
@@ -1487,7 +1473,7 @@ impl ZbugsApp {
             assignee_id: Some(user_id),
             ..UpdateIssueArgs::new(issue_id, now_ms())
         };
-        self.mutate(UPDATE_ISSUE.with(&args), cx);
+        self.mutate(UPDATE_ISSUE.with(args), cx);
     }
 
     /// Adds the label to the issue, or takes it off when it has it.
@@ -1495,9 +1481,9 @@ impl ZbugsApp {
         let has = issue.labels.iter().flatten().any(|l| l.id == label_id);
         let issue_id = issue.id.clone();
         let request = if has {
-            REMOVE_LABEL.with(&RemoveLabelArgs { issue_id, label_id })
+            REMOVE_LABEL.with(RemoveLabelArgs { issue_id, label_id })
         } else {
-            ADD_LABEL.with(&IssueLabelArgs {
+            ADD_LABEL.with(IssueLabelArgs {
                 issue_id,
                 label_id,
                 project_id: None,
@@ -1522,7 +1508,7 @@ impl ZbugsApp {
             key: SKIN_TONE_PREF.to_owned(),
             value: tone.to_string(),
         };
-        self.mutate(SET_USER_PREF.with(&args), cx);
+        self.mutate(SET_USER_PREF.with(args), cx);
     }
 
     /// Takes back the user's reaction with `unicode`, or adds it.
@@ -1543,7 +1529,7 @@ impl ZbugsApp {
             .find(|e| e.creator_id == me && normalize_emoji(&e.value) == key)
         {
             let id = mine.id.clone();
-            self.mutate(REMOVE_EMOJI.with(&id), cx);
+            self.mutate(REMOVE_EMOJI.with(id), cx);
             return;
         }
         let annotation = REACTIONS
@@ -1569,7 +1555,7 @@ impl ZbugsApp {
             Subject::Issue => ADD_EMOJI_TO_ISSUE,
             Subject::Comment => ADD_EMOJI_TO_COMMENT,
         };
-        self.mutate(add.with(&args), cx);
+        self.mutate(add.with(args), cx);
     }
 
     /// Opens the picker with every emoji, to react with any of them.
@@ -1623,7 +1609,7 @@ impl ZbugsApp {
             body,
             created: now_ms(),
         };
-        self.mutate(ADD_COMMENT.with(&args), cx);
+        self.mutate(ADD_COMMENT.with(args), cx);
         self.comment
             .update(cx, |state, cx| state.set_value("", window, cx));
     }
@@ -1735,7 +1721,7 @@ impl ZbugsApp {
                     description: Some(description),
                     ..UpdateIssueArgs::new(id, now)
                 };
-                self.mutate(UPDATE_ISSUE.with(&args), cx);
+                self.mutate(UPDATE_ISSUE.with(args), cx);
             }
             None => {
                 let Some(project_id) = self.project_id() else {
@@ -1755,7 +1741,7 @@ impl ZbugsApp {
                     modified: now,
                     project_id,
                 };
-                self.mutate(CREATE_ISSUE.with(&args), cx);
+                self.mutate(CREATE_ISSUE.with(args), cx);
                 self.select(id, cx);
             }
         }
diff --git a/apps/zbugs-gpui/src/live.rs b/apps/zbugs-gpui/src/live.rs
index 4a1b6ed6da..46710b20ae 100644
--- a/apps/zbugs-gpui/src/live.rs
+++ b/apps/zbugs-gpui/src/live.rs
@@ -12,9 +12,10 @@ use std::cell::RefCell;
 use std::rc::Rc;
 use zbugs_model::Context as Auth;
 use zero_client::client::{MaterializedView, Zero};
+use zero_client::define::QueryRequest;
 use zero_client::ivm::ResultType;
 use zero_client::ttl::Ttl;
-use zero_client::typed::{Query, QueryValue};
+use zero_client::typed::QueryValue;
 
 pub struct Live<T> {
     value: Rc<RefCell<Snapshot<T>>>,
@@ -34,7 +35,7 @@ impl<T: QueryValue + 'static> Live<T> {
     /// rows change, until dropped.
     pub fn new<R: 'static, V: 'static>(
         zero: &Zero<Auth>,
-        query: Query<R, T>,
+        query: QueryRequest<Auth, R, T>,
         ttl: &Ttl,
         cx: &mut Context<V>,
     ) -> Live<T> {
@@ -45,7 +46,7 @@ impl<T: QueryValue + 'static> Live<T> {
         }));
         let (wake, mut woken) = mpsc::unbounded::<()>();
         let view = zero
-            .materialize(query.any(), ttl)
+            .materialize(&query, ttl)
             .expect("a query of the app's schema materializes");
         let v = value.clone();
         let remove = view.add_listener(move |data, result_type, _| {
diff --git a/apps/zbugs-gpui/src/session.rs b/apps/zbugs-gpui/src/session.rs
index 6d3639b9b2..8e8ef8dc8b 100644
--- a/apps/zbugs-gpui/src/session.rs
+++ b/apps/zbugs-gpui/src/session.rs
@@ -130,12 +130,11 @@ impl Session {
         let project = ProjectArgs {
             project_name: ZERO_PROJECT_NAME.into(),
         };
-        let a = auth.as_ref();
         let preloads = vec![
-            zero.preload(ISSUE_PRELOAD_V2.call(&project, a).any(), &ttl),
-            zero.preload(ALL_USERS.call(&(), a).any(), &ttl),
-            zero.preload(ALL_LABELS.call(&(), a).any(), &ttl),
-            zero.preload(ALL_PROJECTS.call(&(), a).any(), &ttl),
+            zero.preload(&ISSUE_PRELOAD_V2.with(project), &ttl),
+            zero.preload(&ALL_USERS.with(()), &ttl),
+            zero.preload(&ALL_LABELS.with(()), &ttl),
+            zero.preload(&ALL_PROJECTS.with(()), &ttl),
         ];
         Session {
             zero: Rc::new(zero),
diff --git a/apps/zbugs-model/Cargo.lock b/apps/zbugs-model/Cargo.lock
index 6ad7049832..63604b5c1d 100644
--- a/apps/zbugs-model/Cargo.lock
+++ b/apps/zbugs-model/Cargo.lock
@@ -19,24 +19,12 @@ dependencies = [
  "r-efi",
 ]
 
-[[package]]
-name = "itoa"
-version = "1.0.19"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3bd1574e617a9a6c1f8f8181bd7e841e1f20e4277607ef28945765188d6284d4"
-
 [[package]]
 name = "libc"
 version = "0.2.191"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "65cd87c9a6d60536580b316ad985726104730a5151c99845f2490428ef91240a"
 
-[[package]]
-name = "memchr"
-version = "2.8.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"
-
 [[package]]
 name = "proc-macro2"
 version = "1.0.107"
@@ -91,19 +79,6 @@ dependencies = [
  "syn",
 ]
 
-[[package]]
-name = "serde_json"
-version = "1.0.154"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e7e9cc8b1b85264074fbcc02a88680c4096b1e47df8f739dceb03bf482f04bd6"
-dependencies = [
- "itoa",
- "memchr",
- "serde",
- "serde_core",
- "zmij",
-]
-
 [[package]]
 name = "syn"
 version = "3.0.10"
@@ -127,16 +102,12 @@ version = "0.0.0"
 dependencies = [
  "getrandom",
  "serde",
- "serde_json",
  "zero-client",
 ]
 
 [[package]]
 name = "zero-client"
 version = "0.1.3"
-
-[[package]]
-name = "zmij"
-version = "1.0.23"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "29666d0abbfad1e3dc4dcf6144730dd3a3ab225bbbdac83319345b1b44ccfc1b"
+dependencies = [
+ "serde",
+]
diff --git a/apps/zbugs-model/Cargo.toml b/apps/zbugs-model/Cargo.toml
index acd09f8ab9..3b88f15e11 100644
--- a/apps/zbugs-model/Cargo.toml
+++ b/apps/zbugs-model/Cargo.toml
@@ -13,10 +13,9 @@ publish = false
 
 [dependencies]
 # The default build: no transport and no storage; the apps choose theirs.
-zero-client = { path = "../../rust/zero-client" }
+zero-client = { path = "../../rust/zero-client", features = ["serde"] }
 getrandom = "0.4"
 serde = { version = "1", features = ["derive"] }
-serde_json = "1"
 
 [lints.rust]
 unsafe_code = "forbid"
diff --git a/apps/zbugs-model/README.md b/apps/zbugs-model/README.md
index 150263e9c7..961a4781fa 100644
--- a/apps/zbugs-model/README.md
+++ b/apps/zbugs-model/README.md
@@ -17,11 +17,13 @@ and depends on this crate by path.
 use zbugs_model::args::{IssueListV2Args, ListContextParams, PageDirection};
 use zbugs_model::{mutators, queries};
 
-let list = queries::ISSUE_LIST_V2.call(&args, auth.as_ref()); // a typed Query<Issue>, named
-let view = zero.materialize(list.any(), &ttl)?;
+// `define_query` and `define_mutator` definitions; the client's context
+// (the logged-in user) comes from `zero`.
+let list = queries::ISSUE_LIST_V2.with(args);
+let view = zero.materialize(&list, &ttl)?;
 let issues = list.read(&view.data())?;
 
-mutators::CREATE_ISSUE.with(&create_args).run(&zero);
+zero.mutate_request(mutators::CREATE_ISSUE.with(create_args));
 // Zero::new(schema::schema(), auth, zbugs_model::client_mutators(), …)
 ```
 
diff --git a/apps/zbugs-model/src/args.rs b/apps/zbugs-model/src/args.rs
index ed5bcb55f2..116ad9d011 100644
--- a/apps/zbugs-model/src/args.rs
+++ b/apps/zbugs-model/src/args.rs
@@ -6,56 +6,10 @@
 //! what the TS side was given.
 
 use crate::schema::IssueVisibility;
-use serde::de::DeserializeOwned;
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
-use zero_client::json::{Object, Value};
+use zero_client::json::Value;
 use zero_client::typed::{Direction, ZeroValue};
 
-/// `value` as JSON.
-pub fn to_value<T: Serialize>(value: &T) -> Value {
-    from_serde(serde_json::to_value(value).expect("arguments encode as JSON"))
-}
-
-/// `value` read as `T`.
-pub fn from_value<T: DeserializeOwned>(value: &Value) -> Result<T, String> {
-    serde_json::from_value(to_serde(value)).map_err(|e| e.to_string())
-}
-
-fn from_serde(value: serde_json::Value) -> Value {
-    match value {
-        serde_json::Value::Null => Value::Null,
-        serde_json::Value::Bool(b) => Value::from(b),
-        serde_json::Value::Number(n) => Value::from(n.as_f64().unwrap_or(f64::NAN)),
-        serde_json::Value::String(s) => Value::from(s),
-        serde_json::Value::Array(a) => Value::Array(a.into_iter().map(from_serde).collect()),
-        serde_json::Value::Object(o) => Value::Object(
-            o.into_iter()
-                .map(|(k, v)| (k, from_serde(v)))
-                .collect::<Object>(),
-        ),
-    }
-}
-
-fn to_serde(value: &Value) -> serde_json::Value {
-    match value {
-        Value::Null => serde_json::Value::Null,
-        Value::Bool(b) => serde_json::Value::Bool(*b),
-        Value::Number(n) => {
-            // Integers as integers, so they read as `i64` fields.
-            if n.fract() == 0.0 && n.abs() < 9_007_199_254_740_992.0 {
-                serde_json::Value::from(*n as i64)
-            } else {
-                serde_json::Number::from_f64(*n).map_or(serde_json::Value::Null, Into::into)
-            }
-        }
-        Value::String(s) => serde_json::Value::String(s.clone()),
-        Value::Array(a) => serde_json::Value::Array(a.iter().map(to_serde).collect()),
-        Value::Object(o) => {
-            serde_json::Value::Object(o.iter().map(|(k, v)| (k.clone(), to_serde(v))).collect())
-        }
-    }
-}
-
 /// `'asc' | 'desc'`.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "lowercase")]
diff --git a/apps/zbugs-model/src/auth.rs b/apps/zbugs-model/src/auth.rs
index 5008e2be12..d74ee5e6fd 100644
--- a/apps/zbugs-model/src/auth.rs
+++ b/apps/zbugs-model/src/auth.rs
@@ -107,8 +107,8 @@ pub(crate) fn must<T>(value: Option<T>) -> Result<T, Error> {
     value.ok_or_else(|| ApplicationError::new("Unexpected undefined value").into())
 }
 
-pub(crate) fn assert_is_logged_in(auth: Option<&AuthData>) -> Result<&AuthData, Error> {
-    auth.ok_or_else(|| {
+pub(crate) fn assert_is_logged_in(auth: &Option<AuthData>) -> Result<&AuthData, Error> {
+    auth.as_ref().ok_or_else(|| {
         mutation_error(
             "User must be logged in for this operation",
             MutationErrorCode::NotLoggedIn,
@@ -117,7 +117,7 @@ pub(crate) fn assert_is_logged_in(auth: Option<&AuthData>) -> Result<&AuthData,
     })
 }
 
-pub(crate) fn is_admin(auth: Option<&AuthData>) -> Result<bool, Error> {
+pub(crate) fn is_admin(auth: &Option<AuthData>) -> Result<bool, Error> {
     Ok(assert_is_logged_in(auth)?.is_crew())
 }
 
@@ -157,7 +157,7 @@ impl Created for Emoji {
 
 pub(crate) fn assert_is_creator_or_admin<R: Created + zero_client::typed::OptionalQueryElement>(
     tx: &Transaction,
-    auth: Option<&AuthData>,
+    auth: &Option<AuthData>,
     query: Query<R>,
     id: &str,
 ) -> Result<(), Error> {
diff --git a/apps/zbugs-model/src/lib.rs b/apps/zbugs-model/src/lib.rs
index 8e10eb09a4..274eb9b3fa 100644
--- a/apps/zbugs-model/src/lib.rs
+++ b/apps/zbugs-model/src/lib.rs
@@ -15,7 +15,7 @@ pub mod queries;
 pub mod schema;
 
 pub use auth::{AuthData, make_id};
-pub use mutators::{Context, MutateRequest, client_mutators};
+pub use mutators::{Context, client_mutators};
 pub use queries::ZERO_PROJECT_NAME;
 
 /// The zero-cache address as the client takes it. zbugs' backend prints it
diff --git a/apps/zbugs-model/src/mutators.rs b/apps/zbugs-model/src/mutators.rs
index 4742a4bac4..4f946422c8 100644
--- a/apps/zbugs-model/src/mutators.rs
+++ b/apps/zbugs-model/src/mutators.rs
@@ -8,90 +8,15 @@ use crate::schema::{
     Comment, CommentUpdate, Emoji, EmojiKey, Issue, IssueKey, IssueLabel, IssueLabelKey,
     IssueNotifications, IssueUpdate, IssueVisibility, Label, UserPref, ViewState, mutate, zql,
 };
-use serde::Serialize;
-use serde::de::DeserializeOwned;
-use zero_client::client::{Error, Mutator, MutatorResult, Transaction, Zero};
-use zero_client::json::Value;
+use zero_client::client::{Error, Mutator, Transaction};
+use zero_client::define::{MutatorDefinition, NamedMutator, define_mutator};
 use zero_client::typed::{ColumnUpdate, RelationshipAggregates};
 
 /// What a mutator is given besides its arguments: who is logged in.
 pub type Context = Option<AuthData>;
 
-type Body<A> = fn(&Transaction, A, Option<&AuthData>) -> Result<(), Error>;
-
-/// A mutator with typed arguments (`defineMutator`).
-pub struct MutatorDef<A> {
-    pub name: &'static str,
-    body: Body<A>,
-}
-
-/// A mutation to run: the mutator's name and its arguments as JSON, for
-/// `Zero::mutate`.
-#[derive(Clone, Debug, PartialEq)]
-pub struct MutateRequest {
-    pub name: &'static str,
-    pub args: Value,
-}
-
-impl MutateRequest {
-    /// Runs the mutation on `zero`: optimistically now, then on the server.
-    pub fn run(self, zero: &Zero<Context>) -> MutatorResult {
-        zero.mutate(self.name, Some(self.args))
-    }
-}
-
-impl<A: Serialize> MutatorDef<A> {
-    /// The mutation of this mutator with `args`.
-    pub fn with(&self, args: &A) -> MutateRequest {
-        MutateRequest {
-            name: self.name,
-            args: to_value(args),
-        }
-    }
-}
-
-impl<A: Serialize + DeserializeOwned + 'static> MutatorDef<A> {
-    /// The client's mutator: reads the JSON arguments as `A`.
-    pub fn mutator(&self) -> Mutator<Context> {
-        let body = self.body;
-        Mutator::new(self.name, move |tx, args, auth: &Context| {
-            let args: A = from_value(args.unwrap_or(&Value::Null))
-                .map_err(zero_client::client::ApplicationError::new)?;
-            body(tx, args, auth.as_ref())?;
-            Ok(None)
-        })
-    }
-
-    /// `args` read as `A` and written back, for the drift test.
-    pub fn reencode(&self, args: Option<&Value>) -> Result<Value, String> {
-        let a: A = from_value(args.unwrap_or(&Value::Null))?;
-        Ok(to_value(&a))
-    }
-}
-
-/// Reads JSON arguments and writes them back.
-pub type Reencode = Box<dyn Fn(Option<&Value>) -> Result<Value, String>>;
-
-/// A mutator of every definition, for the client and the drift test.
-pub struct AnyMutator {
-    pub name: &'static str,
-    pub mutator: Mutator<Context>,
-    pub reencode: Reencode,
-}
-
-fn erase<A: Serialize + DeserializeOwned + 'static>(def: MutatorDef<A>) -> AnyMutator {
-    let mutator = def.mutator();
-    let name = def.name;
-    AnyMutator {
-        name,
-        mutator,
-        reencode: Box::new(move |args| def.reencode(args)),
-    }
-}
-
-pub const CREATE_ISSUE: MutatorDef<CreateIssueArgs> = MutatorDef {
-    name: "issue.create",
-    body: |tx, args, auth| {
+pub const CREATE_ISSUE: MutatorDefinition<CreateIssueArgs, Context> =
+    define_mutator("issue.create", |tx, args, auth| {
         let auth = assert_is_logged_in(auth)?;
         mutate::issue(tx).insert(&Issue {
             id: args.id.clone(),
@@ -125,12 +50,10 @@ pub const CREATE_ISSUE: MutatorDef<CreateIssueArgs> = MutatorDef {
             args.created,
             false,
         )
-    },
-};
+    });
 
-pub const UPDATE_ISSUE: MutatorDef<UpdateIssueArgs> = MutatorDef {
-    name: "issue.update",
-    body: |tx, change, auth| {
+pub const UPDATE_ISSUE: MutatorDefinition<UpdateIssueArgs, Context> =
+    define_mutator("issue.update", |tx, change, auth| {
         // Authorization comes first, so the error does not tell whether a
         // private issue exists.
         assert_is_creator_or_admin(tx, auth, zql::issue(), &change.id)?;
@@ -189,22 +112,18 @@ pub const UPDATE_ISSUE: MutatorDef<UpdateIssueArgs> = MutatorDef {
             )?;
         }
         Ok(())
-    },
-};
+    });
 
-pub const DELETE_ISSUE: MutatorDef<String> = MutatorDef {
-    name: "issue.delete",
-    body: |tx, id, auth| {
+pub const DELETE_ISSUE: MutatorDefinition<String, Context> =
+    define_mutator("issue.delete", |tx, id, auth| {
         assert_is_creator_or_admin(tx, auth, zql::issue(), &id)?;
         mutate::issue(tx).delete(&IssueKey { id })
-    },
-};
+    });
 
 /// Deletes the issues if the user created every one of them (or is an
 /// admin); otherwise none.
-pub const DELETE_ISSUES: MutatorDef<Vec<String>> = MutatorDef {
-    name: "issue.deleteMany",
-    body: |tx, ids, auth| {
+pub const DELETE_ISSUES: MutatorDefinition<Vec<String>, Context> =
+    define_mutator("issue.deleteMany", |tx, ids, auth| {
         assert_is_logged_in(auth)?;
         for id in &ids {
             assert_is_creator_or_admin(tx, auth, zql::issue(), id)?;
@@ -213,32 +132,26 @@ pub const DELETE_ISSUES: MutatorDef<Vec<String>> = MutatorDef {
             mutate::issue(tx).delete(&IssueKey { id })?;
         }
         Ok(())
-    },
-};
+    });
 
-pub const ADD_LABEL: MutatorDef<IssueLabelArgs> = MutatorDef {
-    name: "issue.addLabel",
-    body: |tx, args, auth| {
+pub const ADD_LABEL: MutatorDefinition<IssueLabelArgs, Context> =
+    define_mutator("issue.addLabel", |tx, args, auth| {
         assert_is_creator_or_admin(tx, auth, zql::issue(), &args.issue_id)?;
         let project_id = issue_project_id(tx, &args.issue_id)?;
         mutate::issue_label(tx).insert(&issue_label(args.issue_id, args.label_id, project_id))
-    },
-};
+    });
 
-pub const REMOVE_LABEL: MutatorDef<RemoveLabelArgs> = MutatorDef {
-    name: "issue.removeLabel",
-    body: |tx, args, auth| {
+pub const REMOVE_LABEL: MutatorDefinition<RemoveLabelArgs, Context> =
+    define_mutator("issue.removeLabel", |tx, args, auth| {
         assert_is_creator_or_admin(tx, auth, zql::issue(), &args.issue_id)?;
         mutate::issue_label(tx).delete(&IssueLabelKey {
             label_id: args.label_id,
             issue_id: args.issue_id,
         })
-    },
-};
+    });
 
-pub const UPDATE_NOTIFICATION: MutatorDef<NotificationUpdateArgs> = MutatorDef {
-    name: "notification.update",
-    body: |tx, args, auth| {
+pub const UPDATE_NOTIFICATION: MutatorDefinition<NotificationUpdateArgs, Context> =
+    define_mutator("notification.update", |tx, args, auth| {
         let auth = assert_is_logged_in(auth)?;
         update_issue_notification(
             tx,
@@ -248,30 +161,26 @@ pub const UPDATE_NOTIFICATION: MutatorDef<NotificationUpdateArgs> = MutatorDef {
             args.created,
             true,
         )
-    },
-};
+    });
 
-pub const ADD_EMOJI_TO_ISSUE: MutatorDef<AddEmojiArgs> = MutatorDef {
-    name: "emoji.addToIssue",
-    body: |tx, args, auth| add_emoji(tx, EmojiSubject::Issue, args, auth),
-};
+pub const ADD_EMOJI_TO_ISSUE: MutatorDefinition<AddEmojiArgs, Context> =
+    define_mutator("emoji.addToIssue", |tx, args, auth| {
+        add_emoji(tx, EmojiSubject::Issue, args, auth)
+    });
 
-pub const ADD_EMOJI_TO_COMMENT: MutatorDef<AddEmojiArgs> = MutatorDef {
-    name: "emoji.addToComment",
-    body: |tx, args, auth| add_emoji(tx, EmojiSubject::Comment, args, auth),
-};
+pub const ADD_EMOJI_TO_COMMENT: MutatorDefinition<AddEmojiArgs, Context> =
+    define_mutator("emoji.addToComment", |tx, args, auth| {
+        add_emoji(tx, EmojiSubject::Comment, args, auth)
+    });
 
-pub const REMOVE_EMOJI: MutatorDef<String> = MutatorDef {
-    name: "emoji.remove",
-    body: |tx, id, auth| {
+pub const REMOVE_EMOJI: MutatorDefinition<String, Context> =
+    define_mutator("emoji.remove", |tx, id, auth| {
         assert_is_creator_or_admin(tx, auth, zql::emoji(), &id)?;
         mutate::emoji(tx).delete(&EmojiKey { id })
-    },
-};
+    });
 
-pub const ADD_COMMENT: MutatorDef<AddCommentArgs> = MutatorDef {
-    name: "comment.add",
-    body: |tx, args, auth| {
+pub const ADD_COMMENT: MutatorDefinition<AddCommentArgs, Context> =
+    define_mutator("comment.add", |tx, args, auth| {
         let creator_id = assert_is_logged_in(auth)?.sub.clone();
         assert_user_can_see_issue(tx, &creator_id, &args.issue_id)?;
         mutate::comment(tx).insert(&Comment {
@@ -293,31 +202,25 @@ pub const ADD_COMMENT: MutatorDef<AddCommentArgs> = MutatorDef {
             args.created,
             false,
         )
-    },
-};
+    });
 
-pub const EDIT_COMMENT: MutatorDef<EditCommentArgs> = MutatorDef {
-    name: "comment.edit",
-    body: |tx, args, auth| {
+pub const EDIT_COMMENT: MutatorDefinition<EditCommentArgs, Context> =
+    define_mutator("comment.edit", |tx, args, auth| {
         assert_is_creator_or_admin(tx, auth, zql::comment(), &args.id)?;
         mutate::comment(tx).update(&CommentUpdate {
             body: Some(args.body),
             ..CommentUpdate::new(args.id)
         })
-    },
-};
+    });
 
-pub const REMOVE_COMMENT: MutatorDef<String> = MutatorDef {
-    name: "comment.remove",
-    body: |tx, id, auth| {
+pub const REMOVE_COMMENT: MutatorDefinition<String, Context> =
+    define_mutator("comment.remove", |tx, id, auth| {
         assert_is_creator_or_admin(tx, auth, zql::comment(), &id)?;
         mutate::comment(tx).delete(&crate::schema::CommentKey { id })
-    },
-};
+    });
 
-pub const CREATE_LABEL: MutatorDef<CreateLabelArgs> = MutatorDef {
-    name: "label.create",
-    body: |tx, args, auth| {
+pub const CREATE_LABEL: MutatorDefinition<CreateLabelArgs, Context> =
+    define_mutator("label.create", |tx, args, auth| {
         if !is_admin(auth)? {
             return Err(mutation_error(
                 "Only admins can create labels",
@@ -326,12 +229,10 @@ pub const CREATE_LABEL: MutatorDef<CreateLabelArgs> = MutatorDef {
             ));
         }
         mutate::label(tx).insert(&label(args.id, args.name, args.project_id))
-    },
-};
+    });
 
-pub const CREATE_AND_ADD_LABEL: MutatorDef<CreateAndAddLabelArgs> = MutatorDef {
-    name: "label.createAndAddToIssue",
-    body: |tx, args, auth| {
+pub const CREATE_AND_ADD_LABEL: MutatorDefinition<CreateAndAddLabelArgs, Context> =
+    define_mutator("label.createAndAddToIssue", |tx, args, auth| {
         if !is_admin(auth)? {
             return Err(mutation_error(
                 "Only admins can create labels",
@@ -346,59 +247,54 @@ pub const CREATE_AND_ADD_LABEL: MutatorDef<CreateAndAddLabelArgs> = MutatorDef {
             project_id.clone(),
         ))?;
         mutate::issue_label(tx).insert(&issue_label(args.issue_id, args.label_id, project_id))
-    },
-};
+    });
 
-pub const SET_VIEW_STATE: MutatorDef<ViewStateArgs> = MutatorDef {
-    name: "viewState.set",
-    body: |tx, args, auth| {
+pub const SET_VIEW_STATE: MutatorDefinition<ViewStateArgs, Context> =
+    define_mutator("viewState.set", |tx, args, auth| {
         let user_id = assert_is_logged_in(auth)?.sub.clone();
         mutate::view_state(tx).upsert(&ViewState {
             issue_id: args.issue_id,
             user_id,
             viewed: args.viewed,
         })
-    },
-};
+    });
 
-pub const SET_USER_PREF: MutatorDef<UserPrefArgs> = MutatorDef {
-    name: "userPref.set",
-    body: |tx, args, auth| {
+pub const SET_USER_PREF: MutatorDefinition<UserPrefArgs, Context> =
+    define_mutator("userPref.set", |tx, args, auth| {
         let user_id = assert_is_logged_in(auth)?.sub.clone();
         mutate::user_pref(tx).upsert(&UserPref {
             key: args.key,
             user_id,
             value: args.value,
         })
-    },
-};
+    });
 
 /// Every mutator, for the client and the drift test.
-pub fn all() -> Vec<AnyMutator> {
+pub fn all() -> Vec<Box<dyn NamedMutator<Context>>> {
     vec![
-        erase(CREATE_ISSUE),
-        erase(UPDATE_ISSUE),
-        erase(DELETE_ISSUE),
-        erase(DELETE_ISSUES),
-        erase(ADD_LABEL),
-        erase(REMOVE_LABEL),
-        erase(UPDATE_NOTIFICATION),
-        erase(ADD_EMOJI_TO_ISSUE),
-        erase(ADD_EMOJI_TO_COMMENT),
-        erase(REMOVE_EMOJI),
-        erase(ADD_COMMENT),
-        erase(EDIT_COMMENT),
-        erase(REMOVE_COMMENT),
-        erase(CREATE_LABEL),
-        erase(CREATE_AND_ADD_LABEL),
-        erase(SET_VIEW_STATE),
-        erase(SET_USER_PREF),
+        Box::new(CREATE_ISSUE),
+        Box::new(UPDATE_ISSUE),
+        Box::new(DELETE_ISSUE),
+        Box::new(DELETE_ISSUES),
+        Box::new(ADD_LABEL),
+        Box::new(REMOVE_LABEL),
+        Box::new(UPDATE_NOTIFICATION),
+        Box::new(ADD_EMOJI_TO_ISSUE),
+        Box::new(ADD_EMOJI_TO_COMMENT),
+        Box::new(REMOVE_EMOJI),
+        Box::new(ADD_COMMENT),
+        Box::new(EDIT_COMMENT),
+        Box::new(REMOVE_COMMENT),
+        Box::new(CREATE_LABEL),
+        Box::new(CREATE_AND_ADD_LABEL),
+        Box::new(SET_VIEW_STATE),
+        Box::new(SET_USER_PREF),
     ]
 }
 
 /// The client's mutators: every one, so pending mutations replay by name.
 pub fn client_mutators() -> Vec<Mutator<Context>> {
-    all().into_iter().map(|m| m.mutator).collect()
+    all().iter().map(|m| m.mutator()).collect()
 }
 
 fn label(id: String, name: String, project_id: String) -> Label {
@@ -447,7 +343,7 @@ fn add_emoji(
     tx: &Transaction,
     subject: EmojiSubject,
     args: AddEmojiArgs,
-    auth: Option<&AuthData>,
+    auth: &Context,
 ) -> Result<(), Error> {
     let creator_id = assert_is_logged_in(auth)?.sub.clone();
     match subject {
diff --git a/apps/zbugs-model/src/queries.rs b/apps/zbugs-model/src/queries.rs
index 39aab55e2c..1a080b72ef 100644
--- a/apps/zbugs-model/src/queries.rs
+++ b/apps/zbugs-model/src/queries.rs
@@ -1,85 +1,22 @@
 //! The queries of `apps/zbugs/shared/queries.ts`. The drift test checks
 //! that each builds the same AST as its TS definition.
 //!
-//! Each is a [`NamedQuery`]: the client builds its AST for local results
-//! and sends its name and arguments, which zero-cache asks the API server
-//! to run with the TS definition.
+//! Each is a [`QueryDefinition`]: the client builds its AST for local
+//! results and sends its name and arguments, which zero-cache asks the API
+//! server to run with the TS definition.
 
 use crate::args::*;
-use crate::auth::AuthData;
+use crate::mutators::Context;
 use crate::schema::{
     Comment, Emoji, Issue, IssueLabel, Label, Project, User, UserPref, UserRole, ViewState, zql,
 };
+use zero_client::define::{NamedQuery, QueryDefinition, define_query};
 use zero_client::json::Value;
 use zero_client::like::escape_like;
 use zero_client::typed::{Condition, Direction, ExistsOptions, Query, SimpleOperator, ZeroRow};
 
 pub const ZERO_PROJECT_NAME: &str = "Zero";
 
-/// A query the server runs by name (`defineQuery`): `A` is its argument,
-/// `()` for none.
-pub struct NamedQuery<A, R, T = Vec<R>> {
-    pub name: &'static str,
-    build: fn(&A, Option<&AuthData>) -> Query<R, T>,
-    encode: fn(&A) -> Vec<Value>,
-}
-
-impl<A, R, T> NamedQuery<A, R, T> {
-    /// The query for `args`, as the logged-in user (`auth`) sees it.
-    pub fn call(&self, args: &A, auth: Option<&AuthData>) -> Query<R, T> {
-        let q = (self.build)(args, auth);
-        Query::from_any(q.into_any().name_and_args(self.name, (self.encode)(args)))
-    }
-}
-
-fn no_args(_: &()) -> Vec<Value> {
-    Vec::new()
-}
-
-fn one_arg<A: serde::Serialize>(args: &A) -> Vec<Value> {
-    vec![to_value(args)]
-}
-
-/// Builds a query from JSON arguments, with the arguments as encoded.
-pub type BuildAny =
-    Box<dyn Fn(&[Value], Option<&AuthData>) -> Result<(Query<()>, Vec<Value>), String>>;
-
-/// A query of every query's definition, for the drift test: from the JSON
-/// arguments, the query and the arguments as this side encodes them.
-pub struct AnyNamedQuery {
-    pub name: &'static str,
-    pub build: BuildAny,
-}
-
-fn erase<A: serde::de::DeserializeOwned + 'static, R: 'static, T: 'static>(
-    q: NamedQuery<A, R, T>,
-    decode: fn(&[Value]) -> Result<A, String>,
-) -> AnyNamedQuery {
-    AnyNamedQuery {
-        name: q.name,
-        build: Box::new(move |args, auth| {
-            let a = decode(args)?;
-            let built = q.call(&a, auth);
-            Ok((Query::from_any(built.into_any()), (q.encode)(&a)))
-        }),
-    }
-}
-
-fn decode_none(args: &[Value]) -> Result<(), String> {
-    if args.is_empty() {
-        Ok(())
-    } else {
-        Err(format!("expected no arguments, got {}", args.len()))
-    }
-}
-
-fn decode_one<A: serde::de::DeserializeOwned>(args: &[Value]) -> Result<A, String> {
-    match args {
-        [a] => from_value(a),
-        _ => Err(format!("expected one argument, got {}", args.len())),
-    }
-}
-
 /// The string when JS would take it as true: neither `None` nor empty.
 fn truthy(s: Option<&str>) -> Option<&str> {
     s.filter(|s| !s.is_empty())
@@ -142,18 +79,18 @@ fn labels_query(project_name: &str, order_by: Option<SortDirection>) -> Query<La
     }
 }
 
-fn role(auth: Option<&AuthData>) -> Option<UserRole> {
-    auth.map(|a| a.role)
+fn role(auth: &Context) -> Option<UserRole> {
+    auth.as_ref().map(|a| a.role)
 }
 
 /// The user's own rows of a per-user relationship, or none when logged
 /// out.
 fn own<R: ZeroRow, T>(
     q: Query<R, T>,
-    auth: Option<&AuthData>,
+    auth: &Context,
     user_id: zero_client::typed::Column<R, String>,
 ) -> Query<R, T> {
-    match truthy(auth.map(|a| a.sub.as_str())) {
+    match truthy(auth.as_ref().map(|a| a.sub.as_str())) {
         Some(sub) => q.where_eq(user_id, sub.to_owned()),
         None => always_false(q),
     }
@@ -173,56 +110,38 @@ fn crew(q: Query<User>) -> Query<User> {
     })
 }
 
-pub const ALL_LABELS: NamedQuery<(), Label> = NamedQuery {
-    name: "allLabels",
-    build: |_, _| zql::label(),
-    encode: no_args,
-};
+pub const ALL_LABELS: QueryDefinition<(), Context, Label> =
+    define_query("allLabels", |_, _| zql::label());
 
-pub const ALL_USERS: NamedQuery<(), User> = NamedQuery {
-    name: "allUsers",
-    build: |_, _| zql::user(),
-    encode: no_args,
-};
+pub const ALL_USERS: QueryDefinition<(), Context, User> =
+    define_query("allUsers", |_, _| zql::user());
 
-pub const ALL_PROJECTS: NamedQuery<(), Project> = NamedQuery {
-    name: "allProjects",
-    build: |_, _| zql::project(),
-    encode: no_args,
-};
+pub const ALL_PROJECTS: QueryDefinition<(), Context, Project> =
+    define_query("allProjects", |_, _| zql::project());
 
-pub const USER: NamedQuery<String, User, Option<User>> = NamedQuery {
-    name: "user",
-    build: |id, _| zql::user().where_eq(User::ID, id.clone()).one(),
-    encode: one_arg,
-};
+pub const USER: QueryDefinition<String, Context, User, Option<User>> =
+    define_query("user", |id, _| {
+        zql::user().where_eq(User::ID, id.clone()).one()
+    });
 
-pub const CREW_USER: NamedQuery<String, User, Option<User>> = NamedQuery {
-    name: "crewUser",
-    build: |id, _| {
+pub const CREW_USER: QueryDefinition<String, Context, User, Option<User>> =
+    define_query("crewUser", |id, _| {
         zql::user()
             .where_eq(User::ID, id.clone())
             .where_eq(User::ROLE, UserRole::Crew)
             .one()
-    },
-    encode: one_arg,
-};
+    });
 
-pub const LABELS: NamedQuery<ProjectArgs, Label> = NamedQuery {
-    name: "labels",
-    build: |a, _| labels_query(&a.project_name, None),
-    encode: one_arg,
-};
+pub const LABELS: QueryDefinition<ProjectArgs, Context, Label> =
+    define_query("labels", |a, _| labels_query(&a.project_name, None));
 
-pub const LABELS_ORDER_BY_NAME: NamedQuery<LabelsOrderByNameArgs, Label> = NamedQuery {
-    name: "labelsOrderByName",
-    build: |a, _| labels_query(&a.project_name, Some(a.order_by)),
-    encode: one_arg,
-};
+pub const LABELS_ORDER_BY_NAME: QueryDefinition<LabelsOrderByNameArgs, Context, Label> =
+    define_query("labelsOrderByName", |a, _| {
+        labels_query(&a.project_name, Some(a.order_by))
+    });
 
-pub const ISSUE_PRELOAD_V2: NamedQuery<ProjectArgs, Issue> = NamedQuery {
-    name: "issuePreloadV2",
-    build: |a, auth| {
+pub const ISSUE_PRELOAD_V2: QueryDefinition<ProjectArgs, Context, Issue> =
+    define_query("issuePreloadV2", |a, auth| {
         apply_issue_permissions(
             in_project(zql::issue(), Issue::PROJECT, &a.project_name)
                 .related(Issue::LABELS, |l| l)
@@ -241,28 +160,24 @@ pub const ISSUE_PRELOAD_V2: NamedQuery<ProjectArgs, Issue> = NamedQuery {
                 .limit(1000),
             role(auth),
         )
-    },
-    encode: one_arg,
-};
+    });
 
-pub const USER_PREF: NamedQuery<String, UserPref, Option<UserPref>> = NamedQuery {
-    name: "userPref",
-    build: |key, auth| {
+pub const USER_PREF: QueryDefinition<String, Context, UserPref, Option<UserPref>> =
+    define_query("userPref", |key, auth| {
         // `where('userID', auth?.sub)`: `= null` when logged out.
-        let sub = auth.map_or(Value::Null, |a| Value::from(a.sub.as_str()));
+        let sub = auth
+            .as_ref()
+            .map_or(Value::Null, |a| Value::from(a.sub.as_str()));
         where_named(
             zql::user_pref().where_eq(UserPref::KEY, key.clone()),
             "userID",
             sub,
         )
         .one()
-    },
-    encode: one_arg,
-};
+    });
 
-pub const USERS_FOR_PROJECT: NamedQuery<UsersForProjectArgs, User> = NamedQuery {
-    name: "usersForProject",
-    build: |a, _| {
+pub const USERS_FOR_PROJECT: QueryDefinition<UsersForProjectArgs, Context, User> =
+    define_query("usersForProject", |a, _| {
         let q = zql::user();
         if let (true, Some(login)) = (a.disabled, truthy(a.login.as_deref())) {
             return q.where_eq(User::LOGIN, login.to_owned());
@@ -282,15 +197,12 @@ pub const USERS_FOR_PROJECT: NamedQuery<UsersForProjectArgs, User> = NamedQuery
             }
             None => q,
         }
-    },
-    encode: one_arg,
-};
+    });
 
 /// A page of an issue's comments, ordered by (created, id); a backward page
 /// flips the order. `start` is the cursor row.
-pub const COMMENTS_PAGE: NamedQuery<CommentsPageArgs, Comment> = NamedQuery {
-    name: "commentsPage",
-    build: |a, auth| {
+pub const COMMENTS_PAGE: QueryDefinition<CommentsPageArgs, Context, Comment> =
+    define_query("commentsPage", |a, auth| {
         let dir = match a.dir {
             PageDirection::Forward => Direction::Asc,
             PageDirection::Backward => Direction::Desc,
@@ -314,13 +226,10 @@ pub const COMMENTS_PAGE: NamedQuery<CommentsPageArgs, Comment> = NamedQuery {
             );
         }
         q.limit(a.limit)
-    },
-    encode: one_arg,
-};
+    });
 
-pub const COMMENT: NamedQuery<String, Comment, Option<Comment>> = NamedQuery {
-    name: "comment",
-    build: |id, auth| {
+pub const COMMENT: QueryDefinition<String, Context, Comment, Option<Comment>> =
+    define_query("comment", |id, auth| {
         apply_comment_permissions(
             zql::comment()
                 .related(Comment::CREATOR, |u| u)
@@ -329,13 +238,10 @@ pub const COMMENT: NamedQuery<String, Comment, Option<Comment>> = NamedQuery {
             role(auth),
         )
         .one()
-    },
-    encode: one_arg,
-};
+    });
 
-pub const ISSUE_DETAIL: NamedQuery<IssueDetailArgs, Issue, Option<Issue>> = NamedQuery {
-    name: "issueDetail",
-    build: |a, auth| {
+pub const ISSUE_DETAIL: QueryDefinition<IssueDetailArgs, Context, Issue, Option<Issue>> =
+    define_query("issueDetail", |a, auth| {
         apply_issue_permissions(
             where_named(zql::issue(), a.id_field.column(), a.id.json())
                 .related(Issue::PROJECT, |p| p)
@@ -361,51 +267,41 @@ pub const ISSUE_DETAIL: NamedQuery<IssueDetailArgs, Issue, Option<Issue>> = Name
                 .one(),
             role(auth),
         )
-    },
-    encode: one_arg,
-};
+    });
 
-pub const ISSUE_LIST_V2: NamedQuery<IssueListV2Args, Issue> = NamedQuery {
-    name: "issueListV2",
-    build: |a, auth| {
+pub const ISSUE_LIST_V2: QueryDefinition<IssueListV2Args, Context, Issue> =
+    define_query("issueListV2", |a, auth| {
         build_list_query(ListQueryArgs {
             list_context: Some(&a.list_context),
-            user_id: auth.map(|a| a.sub.as_str()),
+            user_id: auth.as_ref().map(|a| a.sub.as_str()),
             role: role(auth),
             limit: a.limit,
             start: a.start.as_ref(),
             dir: a.dir,
             inclusive: a.inclusive.unwrap_or(false),
         })
-    },
-    encode: one_arg,
-};
+    });
 
 /// The number of issues in the list: the same filters and permissions as
 /// `issueListV2`, reduced to a `count()`.
-pub const ISSUE_LIST_COUNT: NamedQuery<IssueListCountArgs, Issue, i64> = NamedQuery {
-    name: "issueListCount",
-    build: |a, auth| filter_list_query(zql::issue(), &a.list_context, role(auth)).count(),
-    encode: one_arg,
-};
+pub const ISSUE_LIST_COUNT: QueryDefinition<IssueListCountArgs, Context, Issue, i64> =
+    define_query("issueListCount", |a, auth| {
+        filter_list_query(zql::issue(), &a.list_context, role(auth)).count()
+    });
 
 /// One issue, for the order to start a list at.
-pub const LIST_ISSUE_BY_ID: NamedQuery<ListIssueByIdArgs, Issue, Option<Issue>> = NamedQuery {
-    name: "listIssueByID",
-    build: |a, auth| {
+pub const LIST_ISSUE_BY_ID: QueryDefinition<ListIssueByIdArgs, Context, Issue, Option<Issue>> =
+    define_query("listIssueByID", |a, auth| {
         let q = build_list_query(ListQueryArgs {
             list_context: Some(&a.list_context),
             role: role(auth),
             ..ListQueryArgs::default()
         });
         where_named(q, a.id_field.column(), a.id_value.json()).one()
-    },
-    encode: one_arg,
-};
+    });
 
-pub const EMOJI_CHANGE: NamedQuery<String, Emoji> = NamedQuery {
-    name: "emojiChange",
-    build: |subject_id, auth| {
+pub const EMOJI_CHANGE: QueryDefinition<String, Context, Emoji> =
+    define_query("emojiChange", |subject_id, auth| {
         let role = role(auth);
         let mut q = zql::emoji().where_eq(Emoji::SUBJECT_ID, subject_id.clone());
         if role != Some(UserRole::Crew) {
@@ -422,14 +318,11 @@ pub const EMOJI_CHANGE: NamedQuery<String, Emoji> = NamedQuery {
             });
         }
         q.related(Emoji::CREATOR, |u| u.one())
-    },
-    encode: one_arg,
-};
+    });
 
 /// Deprecated in zbugs.
-pub const PREV_NEXT: NamedQuery<PrevNextArgs, Issue, Option<Issue>> = NamedQuery {
-    name: "prevNext",
-    build: |a, auth| {
+pub const PREV_NEXT: QueryDefinition<PrevNextArgs, Context, Issue, Option<Issue>> =
+    define_query("prevNext", |a, auth| {
         build_list_query(ListQueryArgs {
             list_context: a.list_context.as_ref(),
             role: role(auth),
@@ -441,29 +334,23 @@ pub const PREV_NEXT: NamedQuery<PrevNextArgs, Issue, Option<Issue>> = NamedQuery
             ..ListQueryArgs::default()
         })
         .one()
-    },
-    encode: one_arg,
-};
+    });
 
 /// Deprecated in zbugs.
-pub const ISSUE_LIST: NamedQuery<IssueListArgs, Issue> = NamedQuery {
-    name: "issueList",
-    build: |a, auth| {
+pub const ISSUE_LIST: QueryDefinition<IssueListArgs, Context, Issue> =
+    define_query("issueList", |a, auth| {
         build_list_query(ListQueryArgs {
             list_context: Some(&a.list_context),
-            user_id: auth.map(|a| a.sub.as_str()),
+            user_id: auth.as_ref().map(|a| a.sub.as_str()),
             role: role(auth),
             limit: Some(a.limit),
             ..ListQueryArgs::default()
         })
-    },
-    encode: one_arg,
-};
+    });
 
 /// Deprecated in zbugs.
-pub const USER_PICKER: NamedQuery<UserPickerArgs, User> = NamedQuery {
-    name: "userPicker",
-    build: |a, _| {
+pub const USER_PICKER: QueryDefinition<UserPickerArgs, Context, User> =
+    define_query("userPicker", |a, _| {
         let q = zql::user();
         if let (true, Some(login)) = (a.disabled, truthy(a.login.as_deref())) {
             return q.where_eq(User::LOGIN, login.to_owned());
@@ -475,33 +362,31 @@ pub const USER_PICKER: NamedQuery<UserPickerArgs, User> = NamedQuery {
             }
             None => q,
         }
-    },
-    encode: one_arg,
-};
+    });
 
 /// Every query, for the drift test.
-pub fn all() -> Vec<AnyNamedQuery> {
+pub fn all() -> Vec<Box<dyn NamedQuery<Context>>> {
     vec![
-        erase(ALL_LABELS, decode_none),
-        erase(ALL_USERS, decode_none),
-        erase(ALL_PROJECTS, decode_none),
-        erase(USER, decode_one),
-        erase(CREW_USER, decode_one),
-        erase(LABELS, decode_one),
-        erase(LABELS_ORDER_BY_NAME, decode_one),
-        erase(ISSUE_PRELOAD_V2, decode_one),
-        erase(USER_PREF, decode_one),
-        erase(USERS_FOR_PROJECT, decode_one),
-        erase(COMMENTS_PAGE, decode_one),
-        erase(COMMENT, decode_one),
-        erase(ISSUE_DETAIL, decode_one),
-        erase(ISSUE_LIST_V2, decode_one),
-        erase(ISSUE_LIST_COUNT, decode_one),
-        erase(LIST_ISSUE_BY_ID, decode_one),
-        erase(EMOJI_CHANGE, decode_one),
-        erase(PREV_NEXT, decode_one),
-        erase(ISSUE_LIST, decode_one),
-        erase(USER_PICKER, decode_one),
+        Box::new(ALL_LABELS),
+        Box::new(ALL_USERS),
+        Box::new(ALL_PROJECTS),
+        Box::new(USER),
+        Box::new(CREW_USER),
+        Box::new(LABELS),
+        Box::new(LABELS_ORDER_BY_NAME),
+        Box::new(ISSUE_PRELOAD_V2),
+        Box::new(USER_PREF),
+        Box::new(USERS_FOR_PROJECT),
+        Box::new(COMMENTS_PAGE),
+        Box::new(COMMENT),
+        Box::new(ISSUE_DETAIL),
+        Box::new(ISSUE_LIST_V2),
+        Box::new(ISSUE_LIST_COUNT),
+        Box::new(LIST_ISSUE_BY_ID),
+        Box::new(EMOJI_CHANGE),
+        Box::new(PREV_NEXT),
+        Box::new(ISSUE_LIST),
+        Box::new(USER_PICKER),
     ]
 }
 
diff --git a/apps/zbugs-model/tests/drift.rs b/apps/zbugs-model/tests/drift.rs
index 37c50d354a..dbb07b7348 100644
--- a/apps/zbugs-model/tests/drift.rs
+++ b/apps/zbugs-model/tests/drift.rs
@@ -48,10 +48,8 @@ fn matches_the_ts_queries_and_mutators() {
 
     let qs = queries::all();
     let ms = mutators::all();
-    let rust_queries: HashMap<&str, &queries::AnyNamedQuery> =
-        qs.iter().map(|q| (q.name, q)).collect();
-    let rust_mutators: HashMap<&str, &mutators::AnyMutator> =
-        ms.iter().map(|m| (m.name, m)).collect();
+    let rust_queries: HashMap<&str, _> = qs.iter().map(|q| (q.name(), q)).collect();
+    let rust_mutators: HashMap<&str, _> = ms.iter().map(|m| (m.name(), m)).collect();
     let (ts_queries, ts_mutators) = (names(&v, "queries"), names(&v, "mutators"));
     for n in &ts_queries {
         if !rust_queries.contains_key(n.as_str()) {
@@ -91,7 +89,7 @@ fn matches_the_ts_queries_and_mutators() {
             .and_then(Value::as_array)
             .cloned()
             .unwrap_or_default();
-        match (q.build)(&args, context(sample).as_ref()) {
+        match q.query_from_json(&args, &context(sample)) {
             Err(e) => failures.push(format!("{label}: {e}")),
             Ok((query, sent)) => {
                 if sent != args {
@@ -101,7 +99,7 @@ fn matches_the_ts_queries_and_mutators() {
                         json::stringify(&Value::Array(args))
                     ));
                 }
-                let any = query.any();
+                let any = &query;
                 if let Some(e) = any.invalid() {
                     failures.push(format!("{label}: invalid query: {e}"));
                 }
@@ -134,19 +132,19 @@ fn check_mutator(label: &str, sample: &Value) -> Vec<String> {
     let name = sample.get("name").and_then(Value::as_str).unwrap();
     let args = sample.get("args");
     let all = mutators::all();
-    let def = all.iter().find(|m| m.name == name).unwrap();
-    match (def.reencode)(args) {
-        Ok(sent) if Some(&sent) == args => {}
+    let def = all.iter().find(|m| m.name() == name).unwrap();
+    match def.reencode(args) {
+        Ok(sent) if sent.as_ref() == args => {}
         Ok(sent) => failures.push(format!(
             "{label}: the arguments encode as {}, not {}",
-            json::stringify(&sent),
+            sent.as_ref().map_or("undefined".into(), json::stringify),
             args.map_or("undefined".into(), json::stringify)
         )),
         Err(e) => failures.push(format!("{label}: the arguments don't read: {e}")),
     }
 
     let schema = schema::schema();
-    let mut ms: Vec<Mutator<mutators::Context>> = all.into_iter().map(|m| m.mutator).collect();
+    let mut ms: Vec<Mutator<mutators::Context>> = all.iter().map(|m| m.mutator()).collect();
     // Puts the sample's rows (`{table: [row]}`) before the mutator runs.
     ms.push(Mutator::new("__drift.seed", |tx, args, _| {
         for (table, rows) in args.and_then(Value::as_object).into_iter().flatten() {
diff --git a/apps/zbugs-rune/Cargo.lock b/apps/zbugs-rune/Cargo.lock
index 2cb846d715..e0c5379e6a 100644
--- a/apps/zbugs-rune/Cargo.lock
+++ b/apps/zbugs-rune/Cargo.lock
@@ -4772,7 +4772,6 @@ version = "0.0.0"
 dependencies = [
  "getrandom 0.4.3",
  "serde",
- "serde_json",
  "zero-client",
 ]
 
@@ -4920,6 +4919,7 @@ dependencies = [
  "futures-util",
  "rusqlite",
  "rustls",
+ "serde",
  "tokio",
  "tokio-tungstenite",
 ]
diff --git a/apps/zbugs-rune/src/main.rs b/apps/zbugs-rune/src/main.rs
index f336d3256c..438d5847f6 100644
--- a/apps/zbugs-rune/src/main.rs
+++ b/apps/zbugs-rune/src/main.rs
@@ -30,10 +30,10 @@ use zbugs_model::mutators::{
     REMOVE_LABEL, SET_USER_PREF, SET_VIEW_STATE, UPDATE_ISSUE, UPDATE_NOTIFICATION,
 };
 use zbugs_model::schema::{Comment, Emoji, Issue, IssueVisibility, Label, Project, User, UserPref};
-use zbugs_model::{AuthData, Context, MutateRequest, ZERO_PROJECT_NAME, make_id, queries};
-use zero_client::client::ConnectionState;
+use zbugs_model::{AuthData, Context, ZERO_PROJECT_NAME, make_id, queries};
+use zero_client::client::{ConnectionState, MutateRequest};
 use zero_client::ivm::ResultType;
-use zero_client::query::AnyQuery;
+use zero_client::query::ZeroQuery;
 
 /// Rows the issue list asks for at a time: as it nears the end, it asks for
 /// this many more.
@@ -225,16 +225,15 @@ fn now_ms() -> f64 {
         .map_or(0.0, |d| d.as_millis() as f64)
 }
 
-fn preload(auth: &Context) -> Vec<AnyQuery> {
+fn preload() -> Vec<Box<dyn ZeroQuery<Context>>> {
     let project = ProjectArgs {
         project_name: ZERO_PROJECT_NAME.to_owned(),
     };
-    let auth = auth.as_ref();
     vec![
-        queries::ISSUE_PRELOAD_V2.call(&project, auth).into_any(),
-        queries::ALL_USERS.call(&(), auth).into_any(),
-        queries::ALL_LABELS.call(&(), auth).into_any(),
-        queries::ALL_PROJECTS.call(&(), auth).into_any(),
+        Box::new(queries::ISSUE_PRELOAD_V2.with(project)),
+        Box::new(queries::ALL_USERS.with(())),
+        Box::new(queries::ALL_LABELS.with(())),
+        Box::new(queries::ALL_PROJECTS.with(())),
     ]
 }
 
@@ -361,19 +360,16 @@ impl App {
         });
         self.sync.watch(
             "projects",
-            |auth: &Context| queries::ALL_PROJECTS.call(&(), auth.as_ref()),
+            queries::ALL_PROJECTS.with(()),
             |s, rows, _, _| s.projects = rows,
         );
         self.watch_project();
         if let Some(sub) = self.auth.as_ref().map(|a| a.sub.clone()) {
-            self.sync.watch(
-                "me",
-                move |auth: &Context| queries::USER.call(&sub, auth.as_ref()),
-                |s, me, _, _| s.me = me,
-            );
+            self.sync
+                .watch("me", queries::USER.with(sub), |s, me, _, _| s.me = me);
             self.sync.watch(
                 "skin-tone",
-                |auth: &Context| queries::USER_PREF.call(&SKIN_TONE_PREF.to_owned(), auth.as_ref()),
+                queries::USER_PREF.with(SKIN_TONE_PREF.to_owned()),
                 |s, pref: Option<UserPref>, _, _| {
                     s.skin_tone = pref.and_then(|p| p.value.parse().ok()).unwrap_or(0);
                 },
@@ -400,7 +396,7 @@ impl App {
         let crew = users(UsersFilter::Crew);
         self.sync.watch(
             "crew",
-            move |auth: &Context| queries::USERS_FOR_PROJECT.call(&crew, auth.as_ref()),
+            queries::USERS_FOR_PROJECT.with(crew),
             |s, mut rows: Vec<User>, _, _| {
                 by_login(&mut rows);
                 s.crew = rows;
@@ -409,7 +405,7 @@ impl App {
         let creators = users(UsersFilter::Creators);
         self.sync.watch(
             "creators",
-            move |auth: &Context| queries::USERS_FOR_PROJECT.call(&creators, auth.as_ref()),
+            queries::USERS_FOR_PROJECT.with(creators),
             |s, mut rows: Vec<User>, _, _| {
                 by_login(&mut rows);
                 s.creators = rows;
@@ -418,7 +414,7 @@ impl App {
         let assignees = users(UsersFilter::Assignees);
         self.sync.watch(
             "assignees",
-            move |auth: &Context| queries::USERS_FOR_PROJECT.call(&assignees, auth.as_ref()),
+            queries::USERS_FOR_PROJECT.with(assignees),
             |s, mut rows: Vec<User>, _, _| {
                 by_login(&mut rows);
                 s.assignees = rows;
@@ -430,7 +426,7 @@ impl App {
         };
         self.sync.watch(
             "project-labels",
-            move |auth: &Context| queries::LABELS_ORDER_BY_NAME.call(&labels, auth.as_ref()),
+            queries::LABELS_ORDER_BY_NAME.with(labels),
             |s, rows, _, _| s.project_labels = rows,
         );
     }
@@ -519,15 +515,12 @@ impl App {
             dir: PageDirection::Forward,
             inclusive: None,
         };
-        self.sync.watch(
-            "issues",
-            move |auth: &Context| queries::ISSUE_LIST_V2.call(&args, auth.as_ref()),
-            apply_issues,
-        );
+        self.sync
+            .watch("issues", queries::ISSUE_LIST_V2.with(args), apply_issues);
         let count = IssueListCountArgs { list_context };
         self.sync.watch(
             "count",
-            move |auth: &Context| queries::ISSUE_LIST_COUNT.call(&count, auth.as_ref()),
+            queries::ISSUE_LIST_COUNT.with(count),
             |s, n, _, _| s.count = Some(n),
         );
     }
@@ -582,7 +575,7 @@ impl App {
         };
         self.sync.watch(
             "detail",
-            move |auth: &Context| queries::ISSUE_DETAIL.call(&args, auth.as_ref()),
+            queries::ISSUE_DETAIL.with(args),
             |s, issue: Option<Issue>, result_type, _| {
                 if let Some(project) = issue.as_ref().and_then(|i| i.project.as_ref()) {
                     s.watch_labels(&project.name);
@@ -607,7 +600,7 @@ impl App {
         };
         self.sync.watch(
             "labels",
-            move |auth: &Context| queries::LABELS_ORDER_BY_NAME.call(&args, auth.as_ref()),
+            queries::LABELS_ORDER_BY_NAME.with(args),
             |s, rows, _, _| s.labels = rows,
         );
     }
@@ -623,7 +616,7 @@ impl App {
         };
         self.sync.watch(
             "comments",
-            move |auth: &Context| queries::COMMENTS_PAGE.call(&args, auth.as_ref()),
+            queries::COMMENTS_PAGE.with(args),
             |s, rows, _, _| s.comments = rows,
         );
     }
@@ -641,7 +634,7 @@ impl App {
 
     fn mutate(&mut self, request: MutateRequest) {
         self.sync.mutate(
-            move |zero| request.run(zero),
+            move |zero| zero.mutate_request(request),
             |s, message| {
                 s.error = Some(message);
             },
@@ -723,7 +716,7 @@ impl App {
         };
         let body = self.comment_edit.text.trim().to_owned();
         if !body.is_empty() {
-            self.mutate(EDIT_COMMENT.with(&EditCommentArgs { id, body }));
+            self.mutate(EDIT_COMMENT.with(EditCommentArgs { id, body }));
         }
     }
 
@@ -731,7 +724,7 @@ impl App {
     pub fn confirmed(&mut self) {
         match self.confirm.take() {
             Some(Confirm::DeleteIssue(id)) => {
-                self.mutate(DELETE_ISSUE.with(&id));
+                self.mutate(DELETE_ISSUE.with(id.clone()));
                 if self.selected.as_ref() == Some(&id) {
                     self.deselect();
                 }
@@ -740,14 +733,14 @@ impl App {
                 if self.selected.as_ref().is_some_and(|id| ids.contains(id)) {
                     self.deselect();
                 }
-                self.mutate(DELETE_ISSUES.with(&ids));
+                self.mutate(DELETE_ISSUES.with(ids));
                 self.toggle_select_mode();
             }
             Some(Confirm::DeleteComment(id)) => {
                 if self.editing_comment.as_ref() == Some(&id) {
                     self.editing_comment = None;
                 }
-                self.mutate(REMOVE_COMMENT.with(&id));
+                self.mutate(REMOVE_COMMENT.with(id));
             }
             None => {}
         }
@@ -767,7 +760,7 @@ impl App {
             return;
         }
         let Some(issue) = &self.detail else { return };
-        self.mutate(CREATE_AND_ADD_LABEL.with(&CreateAndAddLabelArgs {
+        self.mutate(CREATE_AND_ADD_LABEL.with(CreateAndAddLabelArgs {
             issue_id: issue.id.clone(),
             label_id: make_id(),
             label_name: name,
@@ -783,7 +776,7 @@ impl App {
             open: Some(!issue.open),
             ..UpdateIssueArgs::new(issue.id.clone(), now_ms())
         };
-        self.mutate(UPDATE_ISSUE.with(&args));
+        self.mutate(UPDATE_ISSUE.with(args));
     }
 
     /// Opens `picker`, or closes it when it's open.
@@ -825,7 +818,7 @@ impl App {
                             // server's clock says.
                             viewed: now_ms().max(issue.modified),
                         };
-                        s.mutate(SET_VIEW_STATE.with(&args));
+                        s.mutate(SET_VIEW_STATE.with(args));
                     }
                 });
             });
@@ -847,7 +840,7 @@ impl App {
             visibility: Some(visibility),
             ..UpdateIssueArgs::new(issue.id.clone(), now_ms())
         };
-        self.mutate(UPDATE_ISSUE.with(&args));
+        self.mutate(UPDATE_ISSUE.with(args));
     }
 
     /// Whether the user gets notifications about the issue.
@@ -873,7 +866,7 @@ impl App {
             },
             created: now_ms(),
         };
-        self.mutate(UPDATE_NOTIFICATION.with(&args));
+        self.mutate(UPDATE_NOTIFICATION.with(args));
     }
 
     /// Shows emoji in this skin tone (0 to 5, light to dark after the
@@ -884,7 +877,7 @@ impl App {
             key: SKIN_TONE_PREF.to_owned(),
             value: tone.to_string(),
         };
-        self.mutate(SET_USER_PREF.with(&args));
+        self.mutate(SET_USER_PREF.with(args));
     }
 
     pub fn toggle_picker(&mut self, picker: Picker) {
@@ -911,7 +904,7 @@ impl App {
             assignee_id: Some(assignee.map(|u| u.id.clone())),
             ..UpdateIssueArgs::new(issue.id.clone(), now_ms())
         };
-        self.mutate(UPDATE_ISSUE.with(&args));
+        self.mutate(UPDATE_ISSUE.with(args));
     }
 
     /// Adds the label to the issue, or removes it. The menu stays open for
@@ -921,9 +914,9 @@ impl App {
         let has = issue.labels.iter().flatten().any(|l| l.id == label_id);
         let (issue_id, label_id) = (issue.id.clone(), label_id.to_owned());
         self.mutate(if has {
-            REMOVE_LABEL.with(&RemoveLabelArgs { issue_id, label_id })
+            REMOVE_LABEL.with(RemoveLabelArgs { issue_id, label_id })
         } else {
-            ADD_LABEL.with(&IssueLabelArgs {
+            ADD_LABEL.with(IssueLabelArgs {
                 issue_id,
                 label_id,
                 project_id: None,
@@ -956,7 +949,7 @@ impl App {
             .find(|e| e.creator_id == sub && e.value == value);
         if let Some(e) = mine {
             let id = e.id.clone();
-            self.mutate(REMOVE_EMOJI.with(&id));
+            self.mutate(REMOVE_EMOJI.with(id));
             return;
         }
         // Its CLDR name, as the web picker sends it.
@@ -977,9 +970,9 @@ impl App {
             created: now_ms(),
         };
         self.mutate(if on_issue {
-            ADD_EMOJI_TO_ISSUE.with(&args)
+            ADD_EMOJI_TO_ISSUE.with(args)
         } else {
-            ADD_EMOJI_TO_COMMENT.with(&args)
+            ADD_EMOJI_TO_COMMENT.with(args)
         });
     }
 
@@ -990,7 +983,7 @@ impl App {
         if body.is_empty() {
             return;
         }
-        self.mutate(ADD_COMMENT.with(&AddCommentArgs {
+        self.mutate(ADD_COMMENT.with(AddCommentArgs {
             id: make_id(),
             issue_id: id,
             body,
@@ -1038,14 +1031,14 @@ impl App {
                 description: Some(description),
                 ..UpdateIssueArgs::new(issue.id.clone(), now)
             };
-            self.mutate(UPDATE_ISSUE.with(&args));
+            self.mutate(UPDATE_ISSUE.with(args));
         } else {
             let Some(project) = self.project() else {
                 self.sheet_error = Some("The project hasn't synced yet.".into());
                 return;
             };
             let id = make_id();
-            self.mutate(CREATE_ISSUE.with(&CreateIssueArgs {
+            self.mutate(CREATE_ISSUE.with(CreateIssueArgs {
                 id: id.clone(),
                 title,
                 description: Some(description),
diff --git a/apps/zbugs-rune/src/sync.rs b/apps/zbugs-rune/src/sync.rs
index 90d04ada9c..e15a4d1e8b 100644
--- a/apps/zbugs-rune/src/sync.rs
+++ b/apps/zbugs-rune/src/sync.rs
@@ -19,12 +19,13 @@ use zero_client::client::{
     ConnectionState, MaterializedView, MutationOutcome, Mutator, MutatorResult, Preload, Zero,
     ZeroOptions, ZeroStorage,
 };
+use zero_client::define::QueryRequest;
 use zero_client::ivm::ResultType;
-use zero_client::query::AnyQuery;
+use zero_client::query::ZeroQuery;
 use zero_client::schema::Schema;
 use zero_client::tokio_transport::{TokioScheduler, TokioSocketFactory};
 use zero_client::ttl::Ttl;
-use zero_client::typed::{Query, QueryValue};
+use zero_client::typed::QueryValue;
 
 /// The app's state, which the sync thread updates.
 pub type Ui<S> = AppHandle<S>;
@@ -61,7 +62,7 @@ pub struct Setup<C: 'static> {
     pub schema: fn() -> Arc<Schema>,
     pub mutators: fn() -> Vec<Mutator<C>>,
     /// The queries to keep synced for a client's life, as zbugs preloads.
-    pub preload: fn(&C) -> Vec<AnyQuery>,
+    pub preload: fn() -> Vec<Box<dyn ZeroQuery<C>>>,
     /// Keeps local stores of one app apart from another's.
     pub storage_key: &'static str,
     /// Where the SQLite replica is kept.
@@ -115,7 +116,7 @@ impl<S: 'static, C: Clone + Send + 'static> SyncThread<S, C> {
     pub fn watch<R: 'static, T: QueryValue + Send + 'static>(
         &self,
         slot: &'static str,
-        query: impl Fn(&C) -> Query<R, T> + Send + 'static,
+        query: QueryRequest<C, R, T>,
         apply: fn(&mut S, T, ResultType, &mut rune::Tx),
     ) {
         self.send(move |w| w.watch(slot, query, apply));
@@ -278,9 +279,9 @@ impl<S: 'static, C: Clone + 'static> Worker<S, C> {
             }
         };
         let ttl = Ttl::seconds(10.0);
-        let preloads = (self.setup.preload)(&session.context)
+        let preloads = (self.setup.preload)()
             .iter()
-            .map(|q| zero.preload(q, &ttl))
+            .map(|q| zero.preload(q.as_ref(), &ttl))
             .collect();
         let (ui, f) = (self.ui.clone(), self.on_connection);
         let state = zero.connection().state();
@@ -303,16 +304,15 @@ impl<S: 'static, C: Clone + 'static> Worker<S, C> {
     fn watch<R: 'static, T: QueryValue + Send + 'static>(
         &mut self,
         slot: &'static str,
-        query: impl Fn(&C) -> Query<R, T> + Send + 'static,
+        query: QueryRequest<C, R, T>,
         apply: fn(&mut S, T, ResultType, &mut rune::Tx),
     ) {
         let ui = self.ui.clone();
         // Built for each client, with its context: logging in changes what
         // a query asks for.
         let remake: Remake<C> = Rc::new(move |zero| {
-            let query = query(zero.context());
-            let view = zero.materialize(query.any(), &Ttl::seconds(10.0)).ok()?;
-            let ui = ui.clone();
+            let view = zero.materialize(&query, &Ttl::seconds(10.0)).ok()?;
+            let (ui, query) = (ui.clone(), query.clone());
             let remove = view.add_listener(move |data, result_type, _| {
                 // Rows the generated types can't read are a bug of the
                 // port; say so rather than show nothing.
diff --git a/rust/Cargo.lock b/rust/Cargo.lock
index 1dd5cf8828..fb83446d8c 100644
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -348,6 +348,36 @@ dependencies = [
  "untrusted",
 ]
 
+[[package]]
+name = "serde"
+version = "1.0.229"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4148590afebada386688f18773da617792bf2ef03ffc1e4cbd2b1d45b023e0ba"
+dependencies = [
+ "serde_core",
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_core"
+version = "1.0.229"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "67dca2c9c51e58a4791a4b1ed58308b39c64224d349a935ab5039aa360942a48"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.229"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e7a5d71263a5a7d47b41f6b3f06ba276f10cc18b0931f1799f710578e2309348"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "sha1"
 version = "0.11.0"
@@ -644,6 +674,7 @@ dependencies = [
  "futures-util",
  "rusqlite",
  "rustls",
+ "serde",
  "tokio",
  "tokio-tungstenite",
 ]
diff --git a/rust/PARITY.md b/rust/PARITY.md
index 2619bea8f9..5e2ec6b4ae 100644
--- a/rust/PARITY.md
+++ b/rust/PARITY.md
@@ -112,22 +112,24 @@ the same store, with the views and preloads moved to the new client.
 Generated code (`zero-rust codegen`) has a row struct per table with
 `Column` and `Relationship` constants, and `zql::<table>()` for its typed
 `Query`. `AnyQuery` is the untyped builder, named by strings; a typed
-query wraps one (`any()`, `into_any()`, `Query::from_any`), which is what
-`materialize`, `run`, and `preload` take.
-
-| JS                                                                  | Rust                                                                                           |
-| ------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------- |
-| `defineQueries(...)`, `defineQuery(...)`                            | not ported: name a query with `AnyQuery::name_and_args(name, args)`                            |
-| `.where('open', true)`                                              | `.where_eq(Issue::OPEN, true)`                                                                 |
-| `.where('title', 'LIKE', '%x%')`                                    | `.where_(Issue::TITLE, SimpleOperator::Like, "%x%".into())`                                    |
-| `.where(({cmp, and, or, not, exists}) => ...)`                      | `.where_expr(\|e\| e.and(vec![...]))`, with `RowExpression`                                    |
-| `.where(({cmp, json}) => cmp(json('metadata', 'tags', 0), 'bug'))`  | `.where_expr(\|e\| e.json(User::METADATA, path).eq("bug".into()))`                             |
-| `.whereExists('labels', q => ...)`                                  | `.where_exists(Issue::LABELS, ExistsOptions::default(), \|q\| ...)`                            |
-| `.related('comments', q => q.limit(10))`                            | `.related(Issue::COMMENTS, \|q\| q.limit(10))`                                                 |
-| `.orderBy('created', 'desc')`, `.limit(n)`, `.start(row)`, `.one()` | `.order_by(Issue::CREATED, Direction::Desc)`, `.limit(n)`, `.start(&row, inclusive)`, `.one()` |
-| `.count()`, `.sum`, `.avg`, `.min`, `.max`                          | the same, with `_json` forms for a JSON path; `count` is an `i64`                              |
-| `.related('comments', q => q.count())`                              | `.related(Issue::COMMENTS, \|q\| q.count())`, read as `row.aggregates.count(Issue::COMMENTS)`  |
-| `.distinct(...)`, `.groupBy(...).count()`                           | `.distinct(vec![...])`, `.group_by(vec![...]).count()`                                         |
+query wraps one (`any()`, `into_any()`, `Query::from_any`). `materialize`,
+`run`, and `preload` take any `ZeroQuery`: an `AnyQuery`, a typed `Query`,
+or a named query's `QueryRequest`, which they build with the client's
+context.
+
+| JS                                                                  | Rust                                                                                                                                          |
+| ------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------- |
+| `defineQueries(...)`, `defineQuery(...)`                            | `define::define_query(name, \|args, ctx\| query)` (`serde` feature), called as `Q.with(args)`; untyped, `AnyQuery::name_and_args(name, args)` |
+| `.where('open', true)`                                              | `.where_eq(Issue::OPEN, true)`                                                                                                                |
+| `.where('title', 'LIKE', '%x%')`                                    | `.where_(Issue::TITLE, SimpleOperator::Like, "%x%".into())`                                                                                   |
+| `.where(({cmp, and, or, not, exists}) => ...)`                      | `.where_expr(\|e\| e.and(vec![...]))`, with `RowExpression`                                                                                   |
+| `.where(({cmp, json}) => cmp(json('metadata', 'tags', 0), 'bug'))`  | `.where_expr(\|e\| e.json(User::METADATA, path).eq("bug".into()))`                                                                            |
+| `.whereExists('labels', q => ...)`                                  | `.where_exists(Issue::LABELS, ExistsOptions::default(), \|q\| ...)`                                                                           |
+| `.related('comments', q => q.limit(10))`                            | `.related(Issue::COMMENTS, \|q\| q.limit(10))`                                                                                                |
+| `.orderBy('created', 'desc')`, `.limit(n)`, `.start(row)`, `.one()` | `.order_by(Issue::CREATED, Direction::Desc)`, `.limit(n)`, `.start(&row, inclusive)`, `.one()`                                                |
+| `.count()`, `.sum`, `.avg`, `.min`, `.max`                          | the same, with `_json` forms for a JSON path; `count` is an `i64`                                                                             |
+| `.related('comments', q => q.count())`                              | `.related(Issue::COMMENTS, \|q\| q.count())`, read as `row.aggregates.count(Issue::COMMENTS)`                                                 |
+| `.distinct(...)`, `.groupBy(...).count()`                           | `.distinct(vec![...])`, `.group_by(vec![...]).count()`                                                                                        |
 
 A view's data is a `ViewValue`; a typed query reads it as its rows with
 `query.read(&view.data())` (or `Vec::<Issue>::from_view`). An unnamed
@@ -137,24 +139,30 @@ never settles, and preloading it does nothing.
 
 ### Mutators
 
-| JS                                                                     | Rust                                                                                   |
-| ---------------------------------------------------------------------- | -------------------------------------------------------------------------------------- |
-| `defineMutator(async ({tx, args, ctx}) => ...)`                        | `Mutator::new(name, \|tx, args, ctx\| ...)`, a synchronous closure over JSON arguments |
-| `await tx.mutate.issue.insert(row)`, `.upsert`, `.update`, `.delete`   | `mutate::issue(tx).insert(&row)?` (generated), or `tx.table("issue").insert(&object)?` |
-| `await tx.run(query)`                                                  | `tx.run(&query)?`                                                                      |
-| `tx.location`, `tx.reason`, `tx.clientID`, `tx.mutationID`, `tx.token` | `location()`, `reason()`, `client_id()`, `mutation_id()`, `token()`                    |
-| `throw new ApplicationError(message, {details})`                       | `Err(ApplicationError { message, details }.into())`                                    |
+| JS                                                                     | Rust                                                                                                                                                                                 |
+| ---------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
+| `defineMutator(async ({tx, args, ctx}) => ...)`                        | `define::define_mutator(name, \|tx, args, ctx\| ...)` (`serde` feature), a synchronous function over typed arguments; untyped, `Mutator::new(name, \|tx, args, ctx\| ...)` over JSON |
+| `zero.mutate(mutators.issue.create(args))`                             | `zero.mutate_request(CREATE_ISSUE.with(args))`, or `zero.mutate(name, args)` with JSON arguments                                                                                     |
+| `await tx.mutate.issue.insert(row)`, `.upsert`, `.update`, `.delete`   | `mutate::issue(tx).insert(&row)?` (generated), or `tx.table("issue").insert(&object)?`                                                                                               |
+| `await tx.run(query)`                                                  | `tx.run(&query)?`                                                                                                                                                                    |
+| `tx.location`, `tx.reason`, `tx.clientID`, `tx.mutationID`, `tx.token` | `location()`, `reason()`, `client_id()`, `mutation_id()`, `token()`                                                                                                                  |
+| `throw new ApplicationError(message, {details})`                       | `Err(ApplicationError { message, details }.into())`                                                                                                                                  |
 
 A mutator runs once optimistically and again on every rebase while it is
 pending, so it must depend only on the transaction, its arguments, and the
-context. Calling a mutator that isn't registered throws in JS; in Rust
-both outcomes are a `ZeroError` saying so, and nothing is written or sent.
+context. A definition is registered with its `mutator()` in `Zero::new`;
+its arguments are read back as its type before the body runs, and
+arguments that don't read fail it with an `ApplicationError`, where JS
+validates them with the definition's schema. Calling a mutator that isn't
+registered throws in JS; in Rust both outcomes are a `ZeroError` saying so, and nothing is written or sent.
 
 ### React and SolidJS
 
 No UI bindings: `useQuery` is a `MaterializedView` and its listener.
 `apps/zbugs-rune` shows how a Rune app binds views to its UI, on the
-shared zbugs model (`apps/zbugs-model`); a GPUI app is in progress.
+shared zbugs model (`apps/zbugs-model`), whose queries and mutators are
+`define_query` and `define_mutator` definitions; `apps/zbugs-gpui` is a
+GPUI app on the same model.
 
 ## How some vectors are compared
 
diff --git a/rust/zero-client/Cargo.toml b/rust/zero-client/Cargo.toml
index 01784a9d3e..314a864683 100644
--- a/rust/zero-client/Cargo.toml
+++ b/rust/zero-client/Cargo.toml
@@ -27,12 +27,18 @@ sqlite = ["dep:rusqlite"]
 # SQLite storage with SQLite compiled in, for platforms without a
 # `libsqlite3`.
 sqlite-bundled = ["sqlite", "rusqlite/bundled"]
+# Typed named queries and mutators (`define`), whose arguments are serde
+# types, and serde for `json::Value`.
+serde = ["dep:serde"]
 
 [dependencies]
 futures-util = { version = "0.3", default-features = false, features = [
   "sink",
 ], optional = true }
 rusqlite = { version = "0.40", default-features = false, optional = true }
+serde = { version = "1", default-features = false, features = [
+  "std",
+], optional = true }
 rustls = { version = "0.23", default-features = false, features = [
   "ring",
   "std",
@@ -53,6 +59,7 @@ all-features = true
 
 # The end-to-end tests' WebSocket client and server.
 [dev-dependencies]
+serde = { version = "1", features = ["derive"] }
 futures-util = { version = "0.3", default-features = false, features = [
   "sink",
 ] }
@@ -79,3 +86,7 @@ required-features = ["tokio-transport"]
 
 [lints]
 workspace = true
+
+[[test]]
+name = "define"
+required-features = ["serde"]
diff --git a/rust/zero-client/src/client/mod.rs b/rust/zero-client/src/client/mod.rs
index 9743380563..4b9c855dd0 100644
--- a/rust/zero-client/src/client/mod.rs
+++ b/rust/zero-client/src/client/mod.rs
@@ -37,4 +37,4 @@ pub use scheduler::*;
 pub use socket::{SocketConnection, SocketEvents, SocketFactory, SocketMessage};
 pub use storage::*;
 pub use transaction::{Reason, TableMutator, Transaction};
-pub use zero::{Connection, Mutator, Zero};
+pub use zero::{Connection, MutateRequest, Mutator, Zero};
diff --git a/rust/zero-client/src/client/zero.rs b/rust/zero-client/src/client/zero.rs
index 183fb045f5..b120c918a3 100644
--- a/rust/zero-client/src/client/zero.rs
+++ b/rust/zero-client/src/client/zero.rs
@@ -10,7 +10,7 @@ use super::transaction::Transaction;
 use super::{ApplicationError, Deferred, Error, Scheduler, SocketFactory};
 use crate::ivm::ViewValue;
 use crate::json::Value;
-use crate::query::AnyQuery;
+use crate::query::{AnyQuery, ZeroQuery};
 use crate::schema::Schema;
 use crate::ttl::Ttl;
 use std::cell::{Cell, RefCell};
@@ -57,6 +57,28 @@ impl<C> Mutator<C> {
     }
 }
 
+/// A mutator applied to its arguments, ready for [`Zero::mutate_request`]
+/// (`MutateRequest` in JS and Swift). A `define_mutator` definition makes
+/// one with `with`.
+#[derive(Clone, Debug, PartialEq)]
+pub struct MutateRequest {
+    /// The mutator's name.
+    pub name: String,
+    /// Its arguments as sent: `None` when it takes none (JS `undefined`).
+    pub args: Option<Value>,
+}
+
+impl MutateRequest {
+    /// A request with arguments already in their JSON form, for example to
+    /// replay a mutation by name. Prefer a definition's `with`.
+    pub fn new(name: impl Into<String>, args: Option<Value>) -> Self {
+        MutateRequest {
+            name: name.into(),
+            args,
+        }
+    }
+}
+
 /// A Zero client: syncs the rows of named queries from zero-cache into a
 /// local replica, keeps materialized views of them current, and runs
 /// mutators optimistically before the server confirms them.
@@ -196,12 +218,17 @@ impl<C: 'static> Zero<C> {
 
     /// A view of the query's rows that stays current. Named queries are
     /// synced from the server; an unnamed one only sees local data.
-    pub fn materialize(&self, query: &AnyQuery, ttl: &Ttl) -> Result<MaterializedView, Error> {
+    pub fn materialize(
+        &self,
+        query: &(impl ZeroQuery<C> + ?Sized),
+        ttl: &Ttl,
+    ) -> Result<MaterializedView, Error> {
+        let query = query.any_query(self.context());
         let e = self.engine();
-        let view = e.event_loop.call(|| e.context.materialize(query, ttl))?;
+        let view = e.event_loop.call(|| e.context.materialize(&query, ttl))?;
         let mut views = self.core.views.borrow_mut();
         views.retain(|(v, _, _)| v.upgrade().is_some_and(|v| !v.is_destroyed()));
-        views.push((view.downgrade(), query.clone(), ttl.clone()));
+        views.push((view.downgrade(), query.into_owned(), ttl.clone()));
         Ok(view)
     }
 
@@ -213,22 +240,24 @@ impl<C: 'static> Zero<C> {
     /// it, so waiting for `Complete` or `Cached` never settles.
     pub fn run(
         &self,
-        query: &AnyQuery,
+        query: &(impl ZeroQuery<C> + ?Sized),
         run_type: RunType,
         ttl: Option<&Ttl>,
     ) -> Deferred<ViewValue> {
+        let query = query.any_query(self.context());
         let e = self.engine();
-        e.event_loop.call(|| e.context.run(query, run_type, ttl))
+        e.event_loop.call(|| e.context.run(&query, run_type, ttl))
     }
 
     /// Keeps the query's rows synced without a view, until `cleanup`.
     /// Preloading an unnamed query does nothing. JS's default `ttl` for a
     /// preload is [`Ttl::DEFAULT_PRELOAD`], not `Ttl::default()`.
-    pub fn preload(&self, query: &AnyQuery, ttl: &Ttl) -> Preload {
+    pub fn preload(&self, query: &(impl ZeroQuery<C> + ?Sized), ttl: &Ttl) -> Preload {
+        let query = query.any_query(self.context());
         let e = self.engine();
-        let preload = e.event_loop.call(|| e.context.preload(query, ttl));
+        let preload = e.event_loop.call(|| e.context.preload(&query, ttl));
         let record = Rc::new(PreloadRecord {
-            query: query.clone(),
+            query: query.into_owned(),
             ttl: ttl.clone(),
             cleanup: RefCell::new(preload.cleanup),
             active: Cell::new(true),
@@ -255,6 +284,13 @@ impl<C: 'static> Zero<C> {
         e.event_loop.call(|| e.mutate(name, args))
     }
 
+    /// [`mutate`](Zero::mutate) of a request, such as a `define_mutator`
+    /// definition applied to its arguments: JS's and Swift's
+    /// `zero.mutate(request)`.
+    pub fn mutate_request(&self, request: MutateRequest) -> MutatorResult {
+        self.mutate(&request.name, request.args)
+    }
+
     /// The app was shown, or hidden. Hidden for
     /// `ZeroOptions::hidden_disconnect_delay_ms`, the client disconnects
     /// until it is shown again.
diff --git a/rust/zero-client/src/define.rs b/rust/zero-client/src/define.rs
new file mode 100644
index 0000000000..0c94bac87a
--- /dev/null
+++ b/rust/zero-client/src/define.rs
@@ -0,0 +1,294 @@
+//! Typed named queries and mutators, behind the `serde` feature:
+//! [`define_query`] and [`define_mutator`] (`defineQuery` in
+//! `packages/zql/src/query/query-registry.ts` and `defineMutator` in
+//! `packages/zql/src/mutate/mutator.ts`, shaped like the Swift client's).
+//!
+//! Each is defined once, by its name in the TS registry the server runs and
+//! a serde argument type, and called with a value of that type: the client
+//! sends the name and the arguments as JSON, as JS does, and reads them back
+//! as the type before a mutator's body runs. The context comes from the
+//! [`Zero`](crate::client::Zero) the request goes to.
+//!
+//! ```
+//! # use zero_client::define::{MutatorDefinition, QueryDefinition, define_mutator, define_query};
+//! # use zero_client::client::{Error, Transaction};
+//! # use zero_client::typed::Query;
+//! # struct Label;
+//! # fn labels_query(project: &str) -> Query<Label> { unimplemented!() }
+//! #[derive(serde::Serialize, serde::Deserialize)]
+//! #[serde(rename_all = "camelCase")]
+//! struct ProjectArgs { project_name: String }
+//!
+//! /// The logged-in user, which `Zero::new` was given.
+//! type Context = Option<String>;
+//!
+//! const LABELS: QueryDefinition<ProjectArgs, Context, Label> =
+//!     define_query("labels", |args, _ctx| labels_query(&args.project_name));
+//! const RENAME: MutatorDefinition<ProjectArgs, Context> =
+//!     define_mutator("project.rename", |tx, args, ctx| Ok(()));
+//!
+//! // zero.materialize(&LABELS.with(ProjectArgs { project_name: "Zero".into() }), &ttl)?;
+//! // zero.mutate_request(RENAME.with(ProjectArgs { project_name: "Zero".into() }));
+//! // Zero::new(schema, context, vec![RENAME.mutator()], ...);
+//! ```
+//!
+//! A definition that takes no arguments takes `()` (or another type with
+//! no fields), which sends none, as JS's `undefined` does.
+
+use crate::client::{ApplicationError, Error, MutateRequest, Mutator, Transaction};
+use crate::ivm::ViewValue;
+use crate::json::{self, Value};
+use crate::query::{AnyQuery, ZeroQuery};
+use crate::typed::{Query, QueryValue, ZeroValueError};
+use serde::Serialize;
+use serde::de::DeserializeOwned;
+use std::borrow::Cow;
+use std::sync::Arc;
+
+/// `args` as sent: `None` for a type without fields that writes `null`,
+/// such as `()`, which stands for no arguments.
+fn encode_args<A: Serialize>(args: &A) -> Option<Value> {
+    let value = json::to_value(args).expect("arguments must encode as JSON");
+    (size_of::<A>() != 0 || !value.is_null()).then_some(value)
+}
+
+/// `args` (none, or one JSON value) read as `A`.
+fn decode_args<A: DeserializeOwned>(args: Option<&Value>) -> Result<A, String> {
+    json::from_value(args.unwrap_or(&Value::Null)).map_err(|e| e.to_string())
+}
+
+/// A named query (`defineQuery`): `A` is its arguments, `C` the client's
+/// context, and `Query<R, T>` what it builds. Make one with
+/// [`define_query`].
+///
+/// The name must match the TS registry entry the server runs: the client
+/// builds the query here for optimistic results, and the server builds its
+/// own from the name and arguments.
+pub struct QueryDefinition<A, C, R, T = Vec<R>> {
+    /// Its name in the TS query registry.
+    pub name: &'static str,
+    body: fn(&A, &C) -> Query<R, T>,
+}
+
+impl<A, C, R, T> Clone for QueryDefinition<A, C, R, T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<A, C, R, T> Copy for QueryDefinition<A, C, R, T> {}
+
+/// A named query: `name` in the TS registry, and the query `body` builds
+/// from the arguments and the client's context.
+pub const fn define_query<A, C, R, T>(
+    name: &'static str,
+    body: fn(&A, &C) -> Query<R, T>,
+) -> QueryDefinition<A, C, R, T> {
+    QueryDefinition { name, body }
+}
+
+impl<A, C, R, T> QueryDefinition<A, C, R, T>
+where
+    A: Serialize + Send + Sync + 'static,
+    C: 'static,
+    R: 'static,
+    T: 'static,
+{
+    /// The query with `args`, ready to materialize, run, or preload.
+    pub fn with(&self, args: A) -> QueryRequest<C, R, T> {
+        let encoded = encode_args(&args).into_iter().collect();
+        let body = self.body;
+        QueryRequest {
+            name: self.name,
+            args: encoded,
+            build: Arc::new(move |context| body(&args, context)),
+        }
+    }
+}
+
+/// Builds a request's query from the client's context.
+type BuildQuery<C, R, T> = Arc<dyn Fn(&C) -> Query<R, T> + Send + Sync>;
+
+/// A [`QueryDefinition`] applied to its arguments: what
+/// [`Zero::materialize`](crate::client::Zero::materialize), `run`, and
+/// `preload` take, which build it with the client's context. It is `Send`,
+/// so an app can make one on one thread for a client on another.
+pub struct QueryRequest<C, R, T = Vec<R>> {
+    name: &'static str,
+    args: Vec<Value>,
+    build: BuildQuery<C, R, T>,
+}
+
+impl<C, R, T> Clone for QueryRequest<C, R, T> {
+    fn clone(&self) -> Self {
+        QueryRequest {
+            name: self.name,
+            args: self.args.clone(),
+            build: self.build.clone(),
+        }
+    }
+}
+
+impl<C, R, T> QueryRequest<C, R, T> {
+    /// The query's name.
+    pub fn name(&self) -> &'static str {
+        self.name
+    }
+
+    /// The arguments as sent: none, or one JSON value.
+    pub fn args(&self) -> &[Value] {
+        &self.args
+    }
+
+    /// The query as `context` sees it, named so the server knows it.
+    pub fn query(&self, context: &C) -> Query<R, T> {
+        let any = (self.build)(context).into_any();
+        Query::from_any(any.name_and_args(self.name, self.args.clone()))
+    }
+}
+
+impl<C, R, T: QueryValue> QueryRequest<C, R, T> {
+    /// Reads a view of this query as its result, as `Query::read` does.
+    pub fn read(&self, view: &ViewValue) -> Result<T, ZeroValueError> {
+        T::from_view(view)
+    }
+}
+
+impl<C, R, T> ZeroQuery<C> for QueryRequest<C, R, T> {
+    fn any_query(&self, context: &C) -> Cow<'_, AnyQuery> {
+        Cow::Owned(self.query(context).into_any())
+    }
+}
+
+/// A named query whose arguments come as JSON, as the server gets them,
+/// whatever its types: for a list of an app's queries, such as a test that
+/// checks them against the TS definitions.
+pub trait NamedQuery<C> {
+    /// Its name in the TS query registry.
+    fn name(&self) -> &'static str;
+
+    /// The query for `args` (none, or one JSON value) read as the
+    /// definition's argument type, as `context` sees it, with the arguments
+    /// as this side sends them.
+    fn query_from_json(
+        &self,
+        args: &[Value],
+        context: &C,
+    ) -> Result<(AnyQuery, Vec<Value>), String>;
+}
+
+impl<A, C, R, T> NamedQuery<C> for QueryDefinition<A, C, R, T>
+where
+    A: Serialize + DeserializeOwned + Send + Sync + 'static,
+    C: 'static,
+    R: 'static,
+    T: 'static,
+{
+    fn name(&self) -> &'static str {
+        self.name
+    }
+
+    fn query_from_json(
+        &self,
+        args: &[Value],
+        context: &C,
+    ) -> Result<(AnyQuery, Vec<Value>), String> {
+        let decoded: A = match args {
+            [] => decode_args(None)?,
+            [a] => decode_args(Some(a))?,
+            _ => return Err(format!("expected at most one argument, got {}", args.len())),
+        };
+        let request = self.with(decoded);
+        Ok((request.query(context).into_any(), request.args))
+    }
+}
+
+type MutatorBody<A, C, O> = fn(&Transaction, A, &C) -> Result<O, Error>;
+
+/// A named mutator (`defineMutator`): `A` is its arguments, `C` the
+/// client's context, and `O` what its optimistic run returns to the
+/// caller's `client` outcome (`()` for nothing). Make one with
+/// [`define_mutator`].
+///
+/// The name must match the TS registry entry the API server runs. The body
+/// runs once optimistically and again on every rebase while the mutation is
+/// pending, so it must only depend on `tx`, the arguments, and the context.
+pub struct MutatorDefinition<A, C, O = ()> {
+    /// Its name in the TS mutator registry.
+    pub name: &'static str,
+    body: MutatorBody<A, C, O>,
+}
+
+impl<A, C, O> Clone for MutatorDefinition<A, C, O> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<A, C, O> Copy for MutatorDefinition<A, C, O> {}
+
+/// A named mutator: `name` in the TS registry, and its `body`.
+pub const fn define_mutator<A, C, O>(
+    name: &'static str,
+    body: MutatorBody<A, C, O>,
+) -> MutatorDefinition<A, C, O> {
+    MutatorDefinition { name, body }
+}
+
+impl<A, C, O> MutatorDefinition<A, C, O>
+where
+    A: Serialize + DeserializeOwned + 'static,
+    C: 'static,
+    O: Serialize + 'static,
+{
+    /// The mutation of this mutator with `args`, for
+    /// [`Zero::mutate_request`](crate::client::Zero::mutate_request).
+    pub fn with(&self, args: A) -> MutateRequest {
+        MutateRequest::new(self.name, encode_args(&args))
+    }
+
+    /// The mutator to register with `Zero::new`, so the client runs it and
+    /// replays it by name. Arguments that don't read as `A` fail it with
+    /// an [`ApplicationError`].
+    pub fn mutator(&self) -> Mutator<C> {
+        let body = self.body;
+        Mutator::new(self.name, move |tx, args, context: &C| {
+            let args: A = decode_args(args).map_err(ApplicationError::new)?;
+            Ok(encode_args(&body(tx, args, context)?))
+        })
+    }
+
+    /// `args` read as `A` and encoded again: what this side would send for
+    /// them.
+    pub fn reencode(&self, args: Option<&Value>) -> Result<Option<Value>, String> {
+        Ok(encode_args(&decode_args::<A>(args)?))
+    }
+}
+
+/// A named mutator whatever its types: for a list of an app's mutators,
+/// to register them all and to check them against the TS definitions.
+pub trait NamedMutator<C> {
+    /// Its name in the TS mutator registry.
+    fn name(&self) -> &'static str;
+    /// [`MutatorDefinition::mutator`].
+    fn mutator(&self) -> Mutator<C>;
+    /// [`MutatorDefinition::reencode`].
+    fn reencode(&self, args: Option<&Value>) -> Result<Option<Value>, String>;
+}
+
+impl<A, C, O> NamedMutator<C> for MutatorDefinition<A, C, O>
+where
+    A: Serialize + DeserializeOwned + 'static,
+    C: 'static,
+    O: Serialize + 'static,
+{
+    fn name(&self) -> &'static str {
+        self.name
+    }
+    fn mutator(&self) -> Mutator<C> {
+        MutatorDefinition::mutator(self)
+    }
+    fn reencode(&self, args: Option<&Value>) -> Result<Option<Value>, String> {
+        MutatorDefinition::reencode(self, args)
+    }
+}
diff --git a/rust/zero-client/src/json/mod.rs b/rust/zero-client/src/json/mod.rs
index d783bcad5e..c622d43185 100644
--- a/rust/zero-client/src/json/mod.rs
+++ b/rust/zero-client/src/json/mod.rs
@@ -3,9 +3,13 @@
 
 pub mod number;
 mod parse;
+#[cfg(feature = "serde")]
+mod serde_value;
 mod stringify;
 mod value;
 
 pub use parse::{MAX_DEPTH, ParseError, TOO_DEEP, parse};
+#[cfg(feature = "serde")]
+pub use serde_value::{SerdeError, from_value, to_value};
 pub use stringify::{stringify, write, write_string};
 pub use value::{Object, Value};
diff --git a/rust/zero-client/src/json/serde_value.rs b/rust/zero-client/src/json/serde_value.rs
new file mode 100644
index 0000000000..43863f8d13
--- /dev/null
+++ b/rust/zero-client/src/json/serde_value.rs
@@ -0,0 +1,642 @@
+//! [`Value`] and serde, behind the `serde` feature: [`to_value`] writes any
+//! `Serialize` type as a value, [`from_value`] reads one back as any
+//! `Deserialize` type, and `Value` and [`Object`] are both themselves.
+//!
+//! A struct's fields are written in the order they are declared, as a JS
+//! object literal keeps its properties, and a JS-property-order object
+//! keeps integer-like keys first. Numbers are `f64`, as in JS: an integer
+//! field reads a number without a fraction that is exactly an integer, and
+//! one past 2^53 isn't exact.
+
+use super::{Object, Value};
+use serde::de::{self, DeserializeOwned, IntoDeserializer, Visitor};
+use serde::ser::{self, Serialize};
+use serde::{Deserialize, Deserializer, Serializer, forward_to_deserialize_any};
+use std::fmt;
+
+/// Why a value couldn't be written or read.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct SerdeError(pub String);
+
+impl fmt::Display for SerdeError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.0)
+    }
+}
+
+impl std::error::Error for SerdeError {}
+
+impl ser::Error for SerdeError {
+    fn custom<T: fmt::Display>(msg: T) -> Self {
+        SerdeError(msg.to_string())
+    }
+}
+
+impl de::Error for SerdeError {
+    fn custom<T: fmt::Display>(msg: T) -> Self {
+        SerdeError(msg.to_string())
+    }
+}
+
+/// `value` as a JSON value.
+pub fn to_value<T: Serialize + ?Sized>(value: &T) -> Result<Value, SerdeError> {
+    value.serialize(ValueSerializer)
+}
+
+/// `value` read as a `T`.
+pub fn from_value<T: DeserializeOwned>(value: &Value) -> Result<T, SerdeError> {
+    T::deserialize(value)
+}
+
+// MARK: Writing
+
+struct ValueSerializer;
+
+/// The largest integer a `f64` holds exactly, 2^53.
+const MAX_EXACT: f64 = 9_007_199_254_740_992.0;
+
+fn variant(name: &str, value: Value) -> Value {
+    let mut o = Object::new();
+    o.insert(name, value);
+    Value::Object(o)
+}
+
+impl Serializer for ValueSerializer {
+    type Ok = Value;
+    type Error = SerdeError;
+    type SerializeSeq = SeqSerializer;
+    type SerializeTuple = SeqSerializer;
+    type SerializeTupleStruct = SeqSerializer;
+    type SerializeTupleVariant = SeqSerializer;
+    type SerializeMap = MapSerializer;
+    type SerializeStruct = MapSerializer;
+    type SerializeStructVariant = MapSerializer;
+
+    fn serialize_bool(self, v: bool) -> Result<Value, SerdeError> {
+        Ok(Value::Bool(v))
+    }
+    fn serialize_i8(self, v: i8) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v.into()))
+    }
+    fn serialize_i16(self, v: i16) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v.into()))
+    }
+    fn serialize_i32(self, v: i32) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v.into()))
+    }
+    fn serialize_i64(self, v: i64) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v as f64))
+    }
+    fn serialize_u8(self, v: u8) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v.into()))
+    }
+    fn serialize_u16(self, v: u16) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v.into()))
+    }
+    fn serialize_u32(self, v: u32) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v.into()))
+    }
+    fn serialize_u64(self, v: u64) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v as f64))
+    }
+    fn serialize_f32(self, v: f32) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v.into()))
+    }
+    fn serialize_f64(self, v: f64) -> Result<Value, SerdeError> {
+        Ok(Value::Number(v))
+    }
+    fn serialize_char(self, v: char) -> Result<Value, SerdeError> {
+        Ok(Value::String(v.to_string()))
+    }
+    fn serialize_str(self, v: &str) -> Result<Value, SerdeError> {
+        Ok(Value::String(v.to_owned()))
+    }
+    fn serialize_bytes(self, v: &[u8]) -> Result<Value, SerdeError> {
+        Ok(Value::Array(
+            v.iter().map(|b| Value::Number((*b).into())).collect(),
+        ))
+    }
+    fn serialize_none(self) -> Result<Value, SerdeError> {
+        Ok(Value::Null)
+    }
+    fn serialize_some<T: Serialize + ?Sized>(self, value: &T) -> Result<Value, SerdeError> {
+        value.serialize(self)
+    }
+    fn serialize_unit(self) -> Result<Value, SerdeError> {
+        Ok(Value::Null)
+    }
+    fn serialize_unit_struct(self, _: &'static str) -> Result<Value, SerdeError> {
+        Ok(Value::Null)
+    }
+    fn serialize_unit_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        variant: &'static str,
+    ) -> Result<Value, SerdeError> {
+        Ok(Value::String(variant.to_owned()))
+    }
+    fn serialize_newtype_struct<T: Serialize + ?Sized>(
+        self,
+        _: &'static str,
+        value: &T,
+    ) -> Result<Value, SerdeError> {
+        value.serialize(self)
+    }
+    fn serialize_newtype_variant<T: Serialize + ?Sized>(
+        self,
+        _: &'static str,
+        _: u32,
+        name: &'static str,
+        value: &T,
+    ) -> Result<Value, SerdeError> {
+        Ok(variant(name, value.serialize(self)?))
+    }
+    fn serialize_seq(self, len: Option<usize>) -> Result<SeqSerializer, SerdeError> {
+        Ok(SeqSerializer {
+            variant: None,
+            items: Vec::with_capacity(len.unwrap_or(0)),
+        })
+    }
+    fn serialize_tuple(self, len: usize) -> Result<SeqSerializer, SerdeError> {
+        self.serialize_seq(Some(len))
+    }
+    fn serialize_tuple_struct(
+        self,
+        _: &'static str,
+        len: usize,
+    ) -> Result<SeqSerializer, SerdeError> {
+        self.serialize_seq(Some(len))
+    }
+    fn serialize_tuple_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        name: &'static str,
+        len: usize,
+    ) -> Result<SeqSerializer, SerdeError> {
+        Ok(SeqSerializer {
+            variant: Some(name),
+            items: Vec::with_capacity(len),
+        })
+    }
+    fn serialize_map(self, _: Option<usize>) -> Result<MapSerializer, SerdeError> {
+        Ok(MapSerializer {
+            variant: None,
+            object: Object::new(),
+            key: None,
+        })
+    }
+    fn serialize_struct(self, _: &'static str, _: usize) -> Result<MapSerializer, SerdeError> {
+        self.serialize_map(None)
+    }
+    fn serialize_struct_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        name: &'static str,
+        _: usize,
+    ) -> Result<MapSerializer, SerdeError> {
+        Ok(MapSerializer {
+            variant: Some(name),
+            object: Object::new(),
+            key: None,
+        })
+    }
+}
+
+struct SeqSerializer {
+    variant: Option<&'static str>,
+    items: Vec<Value>,
+}
+
+impl SeqSerializer {
+    fn push<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), SerdeError> {
+        self.items.push(value.serialize(ValueSerializer)?);
+        Ok(())
+    }
+
+    fn done(self) -> Value {
+        let array = Value::Array(self.items);
+        match self.variant {
+            Some(name) => variant(name, array),
+            None => array,
+        }
+    }
+}
+
+impl ser::SerializeSeq for SeqSerializer {
+    type Ok = Value;
+    type Error = SerdeError;
+    fn serialize_element<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), SerdeError> {
+        self.push(value)
+    }
+    fn end(self) -> Result<Value, SerdeError> {
+        Ok(self.done())
+    }
+}
+
+impl ser::SerializeTuple for SeqSerializer {
+    type Ok = Value;
+    type Error = SerdeError;
+    fn serialize_element<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), SerdeError> {
+        self.push(value)
+    }
+    fn end(self) -> Result<Value, SerdeError> {
+        Ok(self.done())
+    }
+}
+
+impl ser::SerializeTupleStruct for SeqSerializer {
+    type Ok = Value;
+    type Error = SerdeError;
+    fn serialize_field<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), SerdeError> {
+        self.push(value)
+    }
+    fn end(self) -> Result<Value, SerdeError> {
+        Ok(self.done())
+    }
+}
+
+impl ser::SerializeTupleVariant for SeqSerializer {
+    type Ok = Value;
+    type Error = SerdeError;
+    fn serialize_field<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), SerdeError> {
+        self.push(value)
+    }
+    fn end(self) -> Result<Value, SerdeError> {
+        Ok(self.done())
+    }
+}
+
+struct MapSerializer {
+    variant: Option<&'static str>,
+    object: Object,
+    key: Option<String>,
+}
+
+impl MapSerializer {
+    fn done(self) -> Value {
+        let object = Value::Object(self.object);
+        match self.variant {
+            Some(name) => variant(name, object),
+            None => object,
+        }
+    }
+}
+
+impl ser::SerializeMap for MapSerializer {
+    type Ok = Value;
+    type Error = SerdeError;
+    fn serialize_key<T: Serialize + ?Sized>(&mut self, key: &T) -> Result<(), SerdeError> {
+        // A key is a string, as a JS object's property is: a number or a
+        // bool key is written as JS would name it.
+        let key = match key.serialize(ValueSerializer)? {
+            Value::String(s) => s,
+            v @ (Value::Number(_) | Value::Bool(_)) => v.to_string(),
+            v => {
+                return Err(SerdeError(format!(
+                    "a map key must be a string, not {}",
+                    v.type_name()
+                )));
+            }
+        };
+        self.key = Some(key);
+        Ok(())
+    }
+    fn serialize_value<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), SerdeError> {
+        let key = self.key.take().expect("serialize_key comes first");
+        self.object.insert(key, value.serialize(ValueSerializer)?);
+        Ok(())
+    }
+    fn end(self) -> Result<Value, SerdeError> {
+        Ok(self.done())
+    }
+}
+
+impl ser::SerializeStruct for MapSerializer {
+    type Ok = Value;
+    type Error = SerdeError;
+    fn serialize_field<T: Serialize + ?Sized>(
+        &mut self,
+        key: &'static str,
+        value: &T,
+    ) -> Result<(), SerdeError> {
+        self.object.insert(key, value.serialize(ValueSerializer)?);
+        Ok(())
+    }
+    fn end(self) -> Result<Value, SerdeError> {
+        Ok(self.done())
+    }
+}
+
+impl ser::SerializeStructVariant for MapSerializer {
+    type Ok = Value;
+    type Error = SerdeError;
+    fn serialize_field<T: Serialize + ?Sized>(
+        &mut self,
+        key: &'static str,
+        value: &T,
+    ) -> Result<(), SerdeError> {
+        ser::SerializeStruct::serialize_field(self, key, value)
+    }
+    fn end(self) -> Result<Value, SerdeError> {
+        Ok(self.done())
+    }
+}
+
+impl Serialize for Value {
+    fn serialize<S: Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
+        match self {
+            Value::Null => s.serialize_unit(),
+            Value::Bool(b) => s.serialize_bool(*b),
+            // An integer as an integer, so a format with integers keeps it
+            // one.
+            Value::Number(n) if n.fract() == 0.0 && n.abs() < MAX_EXACT => {
+                s.serialize_i64(*n as i64)
+            }
+            Value::Number(n) => s.serialize_f64(*n),
+            Value::String(v) => s.serialize_str(v),
+            Value::Array(a) => s.collect_seq(a),
+            Value::Object(o) => o.serialize(s),
+        }
+    }
+}
+
+impl Serialize for Object {
+    fn serialize<S: Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
+        s.collect_map(self.iter())
+    }
+}
+
+// MARK: Reading
+
+impl<'de> Deserializer<'de> for &'de Value {
+    type Error = SerdeError;
+
+    fn deserialize_any<V: Visitor<'de>>(self, visitor: V) -> Result<V::Value, SerdeError> {
+        match self {
+            Value::Null => visitor.visit_unit(),
+            Value::Bool(b) => visitor.visit_bool(*b),
+            // An exact integer reads as one, so integer fields take it.
+            Value::Number(n) if n.fract() == 0.0 && n.abs() < MAX_EXACT => {
+                if *n < 0.0 {
+                    visitor.visit_i64(*n as i64)
+                } else {
+                    visitor.visit_u64(*n as u64)
+                }
+            }
+            Value::Number(n) => visitor.visit_f64(*n),
+            Value::String(s) => visitor.visit_borrowed_str(s),
+            Value::Array(a) => visitor.visit_seq(de::value::SeqDeserializer::new(a.iter())),
+            Value::Object(o) => visitor.visit_map(de::value::MapDeserializer::new(
+                o.iter().map(|(k, v)| (k.as_str(), v)),
+            )),
+        }
+    }
+
+    fn deserialize_option<V: Visitor<'de>>(self, visitor: V) -> Result<V::Value, SerdeError> {
+        match self {
+            Value::Null => visitor.visit_none(),
+            v => visitor.visit_some(v),
+        }
+    }
+
+    fn deserialize_newtype_struct<V: Visitor<'de>>(
+        self,
+        _: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, SerdeError> {
+        visitor.visit_newtype_struct(self)
+    }
+
+    fn deserialize_enum<V: Visitor<'de>>(
+        self,
+        _: &'static str,
+        _: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, SerdeError> {
+        match self {
+            // A unit variant, by name.
+            Value::String(s) => visitor.visit_enum(s.as_str().into_deserializer()),
+            // Any other variant, as `{"<name>": <its value>}`.
+            Value::Object(o) if o.len() == 1 => {
+                let (name, value) = o.get_index(0).expect("one entry");
+                visitor.visit_enum(EnumAccess { name, value })
+            }
+            v => Err(SerdeError(format!(
+                "expected an enum variant, a string or an object with one key, got {}",
+                v.type_name()
+            ))),
+        }
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf unit unit_struct seq tuple tuple_struct map struct
+        identifier ignored_any
+    }
+}
+
+impl<'de> IntoDeserializer<'de, SerdeError> for &'de Value {
+    type Deserializer = Self;
+    fn into_deserializer(self) -> Self {
+        self
+    }
+}
+
+struct EnumAccess<'de> {
+    name: &'de str,
+    value: &'de Value,
+}
+
+impl<'de> de::EnumAccess<'de> for EnumAccess<'de> {
+    type Error = SerdeError;
+    type Variant = &'de Value;
+    fn variant_seed<V: de::DeserializeSeed<'de>>(
+        self,
+        seed: V,
+    ) -> Result<(V::Value, &'de Value), SerdeError> {
+        let name = seed.deserialize(self.name.into_deserializer())?;
+        Ok((name, self.value))
+    }
+}
+
+impl<'de> de::VariantAccess<'de> for &'de Value {
+    type Error = SerdeError;
+    fn unit_variant(self) -> Result<(), SerdeError> {
+        match self {
+            Value::Null => Ok(()),
+            v => Err(SerdeError(format!(
+                "expected a unit variant, got {}",
+                v.type_name()
+            ))),
+        }
+    }
+    fn newtype_variant_seed<T: de::DeserializeSeed<'de>>(
+        self,
+        seed: T,
+    ) -> Result<T::Value, SerdeError> {
+        seed.deserialize(self)
+    }
+    fn tuple_variant<V: Visitor<'de>>(self, _: usize, visitor: V) -> Result<V::Value, SerdeError> {
+        self.deserialize_seq(visitor)
+    }
+    fn struct_variant<V: Visitor<'de>>(
+        self,
+        _: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, SerdeError> {
+        self.deserialize_map(visitor)
+    }
+}
+
+impl<'de> Deserialize<'de> for Value {
+    fn deserialize<D: Deserializer<'de>>(d: D) -> Result<Value, D::Error> {
+        d.deserialize_any(ValueVisitor)
+    }
+}
+
+impl<'de> Deserialize<'de> for Object {
+    fn deserialize<D: Deserializer<'de>>(d: D) -> Result<Object, D::Error> {
+        match Value::deserialize(d)? {
+            Value::Object(o) => Ok(o),
+            v => Err(de::Error::custom(format!(
+                "expected an object, got {}",
+                v.type_name()
+            ))),
+        }
+    }
+}
+
+struct ValueVisitor;
+
+impl<'de> Visitor<'de> for ValueVisitor {
+    type Value = Value;
+
+    fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("a JSON value")
+    }
+    fn visit_bool<E>(self, v: bool) -> Result<Value, E> {
+        Ok(Value::Bool(v))
+    }
+    fn visit_i64<E>(self, v: i64) -> Result<Value, E> {
+        Ok(Value::Number(v as f64))
+    }
+    fn visit_u64<E>(self, v: u64) -> Result<Value, E> {
+        Ok(Value::Number(v as f64))
+    }
+    fn visit_f64<E>(self, v: f64) -> Result<Value, E> {
+        Ok(Value::Number(v))
+    }
+    fn visit_str<E>(self, v: &str) -> Result<Value, E> {
+        Ok(Value::String(v.to_owned()))
+    }
+    fn visit_string<E>(self, v: String) -> Result<Value, E> {
+        Ok(Value::String(v))
+    }
+    fn visit_unit<E>(self) -> Result<Value, E> {
+        Ok(Value::Null)
+    }
+    fn visit_none<E>(self) -> Result<Value, E> {
+        Ok(Value::Null)
+    }
+    fn visit_some<D: Deserializer<'de>>(self, d: D) -> Result<Value, D::Error> {
+        Value::deserialize(d)
+    }
+    fn visit_seq<A: de::SeqAccess<'de>>(self, mut seq: A) -> Result<Value, A::Error> {
+        let mut items = Vec::with_capacity(seq.size_hint().unwrap_or(0));
+        while let Some(v) = seq.next_element()? {
+            items.push(v);
+        }
+        Ok(Value::Array(items))
+    }
+    fn visit_map<A: de::MapAccess<'de>>(self, mut map: A) -> Result<Value, A::Error> {
+        let mut o = Object::new();
+        while let Some((k, v)) = map.next_entry::<String, Value>()? {
+            o.insert(k, v);
+        }
+        Ok(Value::Object(o))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::json;
+
+    #[derive(Debug, PartialEq, serde::Serialize, serde::Deserialize)]
+    #[serde(rename_all = "camelCase")]
+    struct Args {
+        project_name: String,
+        #[serde(rename = "issueID")]
+        issue_id: Option<String>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        limit: Option<i64>,
+        dir: Dir,
+        ratio: f64,
+        tags: Vec<String>,
+        shape: Shape,
+    }
+
+    #[derive(Debug, PartialEq, serde::Serialize, serde::Deserialize)]
+    #[serde(rename_all = "lowercase")]
+    enum Dir {
+        Asc,
+    }
+
+    #[derive(Debug, PartialEq, serde::Serialize, serde::Deserialize)]
+    enum Shape {
+        Circle { r: u32 },
+        Pair(i32, i32),
+    }
+
+    #[test]
+    fn round_trips_in_declared_field_order() {
+        let args = Args {
+            project_name: "Zero".into(),
+            issue_id: None,
+            limit: Some(-3),
+            dir: Dir::Asc,
+            ratio: 0.5,
+            tags: vec!["a".into()],
+            shape: Shape::Circle { r: 2 },
+        };
+        let v = to_value(&args).unwrap();
+        // Fields in the order they are declared, as `JSON.stringify` writes
+        // an object literal with the same properties.
+        assert_eq!(
+            json::stringify(&v),
+            r#"{"projectName":"Zero","issueID":null,"limit":-3,"dir":"asc","ratio":0.5,"tags":["a"],"shape":{"Circle":{"r":2}}}"#
+        );
+        assert_eq!(from_value::<Args>(&v).unwrap(), args);
+        let pair = to_value(&Shape::Pair(1, -2)).unwrap();
+        assert_eq!(json::stringify(&pair), r#"{"Pair":[1,-2]}"#);
+        assert_eq!(from_value::<Shape>(&pair).unwrap(), Shape::Pair(1, -2));
+    }
+
+    #[test]
+    fn integers_read_only_when_exact() {
+        assert_eq!(from_value::<i64>(&Value::Number(4.0)).unwrap(), 4);
+        assert_eq!(from_value::<u8>(&Value::Number(255.0)).unwrap(), 255);
+        assert!(from_value::<i64>(&Value::Number(4.5)).is_err());
+        assert!(from_value::<u8>(&Value::Number(-1.0)).is_err());
+        assert_eq!(from_value::<f64>(&Value::Number(4.0)).unwrap(), 4.0);
+        // A missing optional field and a null one both read as `None`.
+        let v = json::parse(
+            r#"{"projectName":"Zero","dir":"asc","ratio":1,"tags":[],"shape":{"Pair":[0,0]}}"#,
+        )
+        .unwrap();
+        let args: Args = from_value(&v).unwrap();
+        assert_eq!((args.issue_id, args.limit, args.ratio), (None, None, 1.0));
+        assert!(from_value::<Args>(&json::parse(r#"{"projectName":1}"#).unwrap()).is_err());
+    }
+
+    #[test]
+    fn values_are_themselves() {
+        let text = r#"{"b":[1,2.5,null,true,"x"],"10":{},"a":-7}"#;
+        let v = json::parse(text).unwrap();
+        let again: Value = from_value(&to_value(&v).unwrap()).unwrap();
+        assert_eq!(json::stringify(&again), json::stringify(&v));
+    }
+}
diff --git a/rust/zero-client/src/lib.rs b/rust/zero-client/src/lib.rs
index 1fce93ed96..a0d0196501 100644
--- a/rust/zero-client/src/lib.rs
+++ b/rust/zero-client/src/lib.rs
@@ -17,6 +17,9 @@
 //! - `tls`: `wss://` for that transport, with rustls on `ring`.
 //! - `sqlite`: SQLite storage, `ZeroStorage::Sqlite`, on the system
 //!   `libsqlite3`; `sqlite-bundled` compiles SQLite in.
+//! - `serde`: the `define` module, typed named queries and mutators
+//!   (`define_query`, `define_mutator`) over serde argument types, and
+//!   serde for `json::Value`.
 //!
 //! # Storage
 //!
@@ -92,6 +95,9 @@ pub mod builder;
 pub mod client;
 pub mod compare;
 pub mod decode;
+#[cfg(feature = "serde")]
+#[warn(missing_docs)]
+pub mod define;
 pub mod format;
 pub mod hash;
 pub mod ivm;
diff --git a/rust/zero-client/src/query.rs b/rust/zero-client/src/query.rs
index e6e8fac874..af328eb0cc 100644
--- a/rust/zero-client/src/query.rs
+++ b/rust/zero-client/src/query.rs
@@ -14,9 +14,24 @@ use crate::format::Format;
 use crate::hash::query::hash_of_query_internals;
 use crate::json::{self, Object, Value};
 use crate::schema::{Cardinality, Relationship, RelationshipHop, Schema, ValueType};
+use std::borrow::Cow;
 use std::cell::RefCell;
 use std::sync::Arc;
 
+/// A query a `Zero` materializes, runs, and preloads: an [`AnyQuery`], a
+/// typed `Query`, or (with the `serde` feature) a `QueryRequest` of a
+/// `define_query` definition, which is built with the client's context.
+pub trait ZeroQuery<C> {
+    /// The query, as `context` sees it.
+    fn any_query(&self, context: &C) -> Cow<'_, AnyQuery>;
+}
+
+impl<C> ZeroQuery<C> for AnyQuery {
+    fn any_query(&self, _: &C) -> Cow<'_, AnyQuery> {
+        Cow::Borrowed(self)
+    }
+}
+
 /// The prefix of the aliases the builder gives `exists` subqueries
 /// (`SUBQ_PREFIX` in `packages/zero-protocol/src/ast.ts`).
 pub const SUBQUERY_ALIAS_PREFIX: &str = "zsubq_";
diff --git a/rust/zero-client/src/typed.rs b/rust/zero-client/src/typed.rs
index 6aa54587be..e23a6054b4 100644
--- a/rust/zero-client/src/typed.rs
+++ b/rust/zero-client/src/typed.rs
@@ -1018,6 +1018,12 @@ impl<R: ZeroRow, T> Query<R, T> {
     }
 }
 
+impl<C, R, T> crate::query::ZeroQuery<C> for Query<R, T> {
+    fn any_query(&self, _: &C) -> std::borrow::Cow<'_, AnyQuery> {
+        std::borrow::Cow::Borrowed(&self.any)
+    }
+}
+
 impl<R, T: QueryValue> Query<R, T> {
     /// Reads a view of this query as its result.
     pub fn read(&self, view: &ViewValue) -> Result<T, ZeroValueError> {
diff --git a/rust/zero-client/tests/define.rs b/rust/zero-client/tests/define.rs
new file mode 100644
index 0000000000..043d106aa2
--- /dev/null
+++ b/rust/zero-client/tests/define.rs
@@ -0,0 +1,204 @@
+//! Typed named queries and mutators (`define`): their arguments go out as
+//! the JSON JS sends, the client's context reaches their bodies, and a
+//! mutator reads its arguments back before it runs.
+
+use std::rc::Rc;
+use std::sync::Arc;
+use zero_client::ast::System;
+use zero_client::client::{MutationOutcome, RunType, Transaction, Zero, ZeroOptions};
+use zero_client::define::{
+    MutatorDefinition, NamedMutator, NamedQuery, QueryDefinition, define_mutator, define_query,
+};
+use zero_client::json::{self, Object, Value};
+use zero_client::query::{AnyQuery, ZeroQuery};
+use zero_client::schema::Schema;
+use zero_client::testing::{ManualScheduler, RecordingLogSink};
+use zero_client::ttl::Ttl;
+use zero_client::typed::{Query, SimpleOperator};
+
+fn schema() -> Arc<Schema> {
+    let schema = json::parse(
+        r#"{"tables": {"issue": {"name": "issue", "columns": {
+            "id": {"type": "string"}, "title": {"type": "string"},
+            "owner": {"type": "string"}}, "primaryKey": ["id"]}}}"#,
+    )
+    .unwrap();
+    Arc::new(Schema::from_json(&schema).unwrap())
+}
+
+/// Who is logged in.
+type Context = String;
+
+#[derive(Debug, PartialEq, serde::Serialize, serde::Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct ByTitle {
+    title: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    limit: Option<f64>,
+}
+
+#[derive(serde::Serialize, serde::Deserialize)]
+struct Create {
+    id: String,
+    title: String,
+}
+
+fn issues() -> Query<()> {
+    Query::from_any(AnyQuery::new(schema(), "issue", System::Client))
+}
+
+/// The logged-in user's issues with the title.
+const MINE_BY_TITLE: QueryDefinition<ByTitle, Context, ()> =
+    define_query("issues.mineByTitle", |args, owner| {
+        let q = issues().into_any();
+        let q = q.where_("title", SimpleOperator::Eq, args.title.as_str());
+        Query::from_any(q.where_("owner", SimpleOperator::Eq, owner.as_str()))
+    });
+
+const ALL: QueryDefinition<(), Context, ()> = define_query("issues.all", |(), _| issues());
+
+/// Creates an issue owned by the logged-in user, and returns its id.
+const CREATE: MutatorDefinition<Create, Context, String> =
+    define_mutator("issue.create", |tx: &Transaction, args, owner| {
+        let mut row = Object::new();
+        row.insert("id", Value::from(args.id.as_str()));
+        row.insert("title", Value::from(args.title));
+        row.insert("owner", Value::from(owner.as_str()));
+        tx.table("issue").insert(&row)?;
+        Ok(args.id)
+    });
+
+const CLEAR: MutatorDefinition<(), Context> = define_mutator("issue.clear", |_, (), _| Ok(()));
+
+fn client(owner: &str) -> (Zero<Context>, Rc<ManualScheduler>) {
+    let scheduler = ManualScheduler::new(1_700_000_000_000.0);
+    let zero = Zero::new(
+        schema(),
+        owner.to_owned(),
+        vec![CREATE.mutator(), CLEAR.mutator()],
+        ZeroOptions {
+            log_sink: Some(Rc::new(RecordingLogSink::default())),
+            // Memory stores outlive a client by name: each user gets one.
+            storage_key: Some(owner.to_owned()),
+            ..ZeroOptions::default()
+        },
+        scheduler.clone(),
+        None,
+    )
+    .unwrap();
+    scheduler.run_checkpoints();
+    (zero, scheduler)
+}
+
+#[test]
+fn a_query_request_sends_its_name_and_args_and_builds_with_the_context() {
+    let request = MINE_BY_TITLE.with(ByTitle {
+        title: "Bug".into(),
+        limit: None,
+    });
+    // As JS sends `{title: 'Bug'}`: fields in declaration order, an
+    // optional one left out.
+    assert_eq!(
+        json::stringify(&Value::Array(request.args().to_vec())),
+        r#"[{"title":"Bug"}]"#
+    );
+    let any = request.any_query(&"u1".to_owned()).into_owned();
+    let id = any.custom_query_id().unwrap();
+    assert_eq!(
+        (id.name.as_str(), id.args.as_slice()),
+        ("issues.mineByTitle", request.args())
+    );
+
+    // No arguments sends none, as JS's `undefined`.
+    assert!(ALL.with(()).args().is_empty());
+}
+
+#[test]
+fn views_and_mutators_get_the_clients_context() {
+    let (zero, scheduler) = client("u1");
+    let mine = MINE_BY_TITLE.with(ByTitle {
+        title: "Bug".into(),
+        limit: None,
+    });
+    let view = zero.materialize(&mine, &Ttl::default()).unwrap();
+    let result = zero.mutate_request(CREATE.with(Create {
+        id: "i1".into(),
+        title: "Bug".into(),
+    }));
+    scheduler.run_checkpoints();
+    // The body's return value is the client outcome.
+    assert_eq!(
+        result.client.result().unwrap().unwrap(),
+        MutationOutcome::Success {
+            data: Some(Value::from("i1"))
+        }
+    );
+    let rows = view.data();
+    assert_eq!(rows.entries().len(), 1);
+    assert_eq!(rows.entries()[0].row.get("owner"), Some(&Value::from("u1")));
+
+    // `run` and `preload` take the request too; another user's view of the
+    // same title is empty.
+    let run = zero.run(&mine, RunType::Unknown, None);
+    scheduler.run_checkpoints();
+    assert_eq!(run.result().unwrap().unwrap().entries().len(), 1);
+    let (other, s2) = client("u2");
+    other.mutate_request(CREATE.with(Create {
+        id: "i2".into(),
+        title: "Bug".into(),
+    }));
+    s2.run_checkpoints();
+    let theirs = other.run(&mine, RunType::Unknown, None);
+    s2.run_checkpoints();
+    let theirs = theirs.result().unwrap().unwrap();
+    assert_eq!(theirs.entries()[0].row.get("id"), Some(&Value::from("i2")));
+}
+
+#[test]
+fn a_mutator_reads_its_arguments_back_before_it_runs() {
+    let (zero, scheduler) = client("u1");
+    // A mutation replayed or sent by name with arguments that don't read as
+    // the definition's type fails, as an app error, and writes nothing.
+    let bad = zero.mutate("issue.create", Some(json::parse(r#"{"id": 1}"#).unwrap()));
+    scheduler.run_checkpoints();
+    match bad.client.result().unwrap().unwrap() {
+        MutationOutcome::AppError { message, .. } => {
+            assert!(message.contains("invalid type"), "{message}");
+        }
+        other => panic!("expected an app error, got {other:?}"),
+    }
+    // A mutator without arguments sends none and returns nothing.
+    let clear = CLEAR.with(());
+    assert_eq!(clear.args, None);
+    let cleared = zero.mutate_request(clear);
+    scheduler.run_checkpoints();
+    assert_eq!(
+        cleared.client.result().unwrap().unwrap(),
+        MutationOutcome::Success { data: None }
+    );
+}
+
+#[test]
+fn definitions_take_json_arguments_as_the_server_gets_them() {
+    let ctx = "u1".to_owned();
+    let args = vec![json::parse(r#"{"limit": 3, "title": "Bug"}"#).unwrap()];
+    let (query, sent) = MINE_BY_TITLE.query_from_json(&args, &ctx).unwrap();
+    assert_eq!(
+        json::stringify(&Value::Array(sent)),
+        r#"[{"title":"Bug","limit":3}]"#
+    );
+    assert_eq!(query.custom_query_id().unwrap().name, "issues.mineByTitle");
+    assert!(MINE_BY_TITLE.query_from_json(&[], &ctx).is_err());
+    assert!(ALL.query_from_json(&[], &ctx).unwrap().1.is_empty());
+    assert!(ALL.query_from_json(&[Value::from(1.0)], &ctx).is_err());
+
+    let mutators: Vec<Box<dyn NamedMutator<Context>>> = vec![Box::new(CREATE), Box::new(CLEAR)];
+    let names: Vec<_> = mutators.iter().map(|m| m.name()).collect();
+    assert_eq!(names, ["issue.create", "issue.clear"]);
+    let create = json::parse(r#"{"title": "t", "id": "i1"}"#).unwrap();
+    assert_eq!(
+        json::stringify(&mutators[0].reencode(Some(&create)).unwrap().unwrap()),
+        r#"{"id":"i1","title":"t"}"#
+    );
+    assert_eq!(mutators[1].reencode(None).unwrap(), None);
+}