diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 94050bd..ab18733 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -155,6 +155,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       WASM_PACK: "0.15.0"
+      CARGO_ABOUT: "0.9.2"
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
@@ -165,6 +166,11 @@ jobs:
       - run: |
           curl -sSL "https://github.com/wasm-bindgen/wasm-pack/releases/download/v$WASM_PACK/wasm-pack-v$WASM_PACK-x86_64-unknown-linux-musl.tar.gz" \
             | tar -xz --strip-components=1 -C "$HOME/.cargo/bin" "wasm-pack-v$WASM_PACK-x86_64-unknown-linux-musl/wasm-pack"
+      # `cargo-about` writes the licence notices `pack.sh` puts in the
+      # package, from the same release archives `wasm-pack` comes from.
+      - run: |
+          curl -sSL "https://github.com/EmbarkStudios/cargo-about/releases/download/$CARGO_ABOUT/cargo-about-$CARGO_ABOUT-x86_64-unknown-linux-musl.tar.gz" \
+            | tar -xz --strip-components=1 -C "$HOME/.cargo/bin" "cargo-about-$CARGO_ABOUT-x86_64-unknown-linux-musl/cargo-about"
       # Every command below runs without the workflow's `RUSTFLAGS`: the
       # variable replaces the flags of `.cargo/config.toml` instead of
       # adding to them, and this target would be built without `simd128`
diff --git a/.github/workflows/publish-npm.yml b/.github/workflows/publish-npm.yml
index c59007e..268a510 100644
--- a/.github/workflows/publish-npm.yml
+++ b/.github/workflows/publish-npm.yml
@@ -33,6 +33,7 @@ jobs:
       contents: write
     env:
       WASM_PACK: "0.15.0"
+      CARGO_ABOUT: "0.9.2"
       PLAN: ${{ inputs.plan }}
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
@@ -53,6 +54,11 @@ jobs:
       - run: |
           curl -sSL "https://github.com/wasm-bindgen/wasm-pack/releases/download/v$WASM_PACK/wasm-pack-v$WASM_PACK-x86_64-unknown-linux-musl.tar.gz" \
             | tar -xz --strip-components=1 -C "$HOME/.cargo/bin" "wasm-pack-v$WASM_PACK-x86_64-unknown-linux-musl/wasm-pack"
+      # `cargo-about` writes the licence notices `pack.sh` puts in the
+      # package, from the same release archives `wasm-pack` comes from.
+      - run: |
+          curl -sSL "https://github.com/EmbarkStudios/cargo-about/releases/download/$CARGO_ABOUT/cargo-about-$CARGO_ABOUT-x86_64-unknown-linux-musl.tar.gz" \
+            | tar -xz --strip-components=1 -C "$HOME/.cargo/bin" "cargo-about-$CARGO_ABOUT-x86_64-unknown-linux-musl/cargo-about"
       - run: crates/sqzer-wasm/pack.sh
       # The package carries the workspace version, which dist has already
       # matched against the tag for the binaries. Checked again here
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5e28b6a..9bdd8a1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@
 
 ### Bug Fixes
 
+* **wasm:** the npm package carries `THIRD-PARTY-LICENSES.txt`, the licence notice of every crate compiled into `sqzer_bg.wasm`, generated by `cargo about` from the wasm32 dependency tree as `pack.sh` builds the package. The C library inside `libdeflate-sys` has its own MIT notice there, and `avif-parse`, under MPL-2.0, is listed with its repository. The package shipped its own two licence texts and nothing for the 170-odd crates in the module ([#54](https://github.com/sqzer-dev/sqzer/issues/54))
 * **sqzer:** an explicit quality with no format, on a graphic the portable tier sends to lossless WebP, is reported as what it was: `Output::target` is `Resolved::Lossless` and `Output::lossless` is `true`, where the record said the quality asked for and `lossless: false` over the same lossless bytes. `--json`, `{quality}` in a `--template` and the npm package follow ([#56](https://github.com/sqzer-dev/sqzer/issues/56))
 
 ## 0.3.0
diff --git a/CLAUDE.md b/CLAUDE.md
index 9648d8b..cc59a86 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -60,7 +60,7 @@ cargo build --workspace                                   # portable tier
 cargo build -p sqzer-cli --features native                # needs C libs on PATH / vcpkg
 cargo build -p sqzer-wasm --target wasm32-unknown-unknown # proves portable builds without a libc; needs clang
 (cd crates/sqzer-wasm && wasm-pack test --node)          # the JavaScript API over the fixtures; needs wasm-pack, and no RUSTFLAGS set
-crates/sqzer-wasm/pack.sh                                 # the npm package as a tag publishes it, packed and run from its tarball
+crates/sqzer-wasm/pack.sh                                 # the npm package as a tag publishes it, packed and run from its tarball; needs cargo-about and jq
 cargo test --workspace
 cargo clippy --workspace --all-targets --all-features     # pedantic is on, warnings are errors in CI
 cargo fmt --all
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d219096..fe627f3 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -43,6 +43,10 @@ cargo build -p sqzer-wasm --target wasm32-unknown-unknown
 
 # the browser build's JavaScript API over the fixtures, in Node; needs wasm-pack
 (cd crates/sqzer-wasm && wasm-pack test --node)
+
+# the npm package as a tag publishes it, with the licence notices of every crate in
+# the module; needs wasm-pack, cargo-about (`cargo install cargo-about --features cli`), jq and Node
+crates/sqzer-wasm/pack.sh
 ```
 
 > **Note**: The golden tests compare each encoder's SSIMULACRA2 score on the fixtures against a committed value. If a change moves a score, say why in the PR; do not just update the number.
diff --git a/about.toml b/about.toml
new file mode 100644
index 0000000..a96bbe0
--- /dev/null
+++ b/about.toml
@@ -0,0 +1,116 @@
+# `cargo about` writes the licence notices of everything compiled into a
+# build: `crates/sqzer-wasm/pack.sh` runs it over the npm package into
+# `THIRD-PARTY-LICENSES.txt` with `crates/sqzer-wasm/about.hbs`. The
+# accepted list is the allow-list of `deny.toml`, in the order a crate
+# that offers a choice is taken: a crate that is `MIT OR Apache-2.0`
+# ships its MIT notice.
+accepted = [
+    "MIT",
+    "Apache-2.0",
+    "Apache-2.0 WITH LLVM-exception",
+    "BSD-2-Clause",
+    "BSD-3-Clause",
+    "ISC",
+    "Zlib",
+    "MPL-2.0",
+    "Unicode-3.0",
+    "Unicode-DFS-2016",
+    "CC0-1.0",
+]
+# The package is the wasm32 build; what only a desktop target compiles
+# is not in it. Build scripts and their dependencies (`cc`) do not ship,
+# and neither does `sqzer-wasm` itself, `publish = false`: the package's
+# own licence is next to the file. The four published workspace crates
+# are left out by the template, on their repository.
+targets = ["wasm32-unknown-unknown"]
+ignore-build-dependencies = true
+ignore-dev-dependencies = true
+private = { ignore = true }
+# A notice lives at the root of a crate. Scanned deeper, the tree gave a
+# C fuzzing harness in `qoi` and Rust source headers in `kamadak-exif`
+# as licence texts, each with a notice inside it.
+max-depth = 1
+
+# What the scan cannot read on its own, clarified per crate. Every
+# checksum pins a file's text, not a crate version: a bump keeps working
+# until the notice itself changes, and then `pack.sh` fails until the
+# entry is checked again. `files` are read from the crate as published,
+# `git` from its repository at the commit it was published from, for a
+# crate that ships no notice and keeps one at the root of its repository.
+# Two crates stay on the bare licence text: `simd_helpers` has no notice
+# in its repository either, and `zune-inflate` names no repository.
+
+# Vendors and compiles `libdeflate`, a C library under its own MIT
+# notice, which the crate's Apache-2.0 field does not carry.
+[libdeflate-sys]
+clarify = { license = "Apache-2.0 AND MIT", files = [
+    { path = "LICENSE", license = "Apache-2.0", checksum = "a60eea817514531668d7e00765731449fe14d059d3249e0bc93b36de45f759f2" },
+    { path = "libdeflate/COPYING", license = "MIT", checksum = "4ad69099cb4374836fd27583d9991e2838cd86b6e4666ab26b2d32582c91e73a" },
+] }
+
+# Names its licence by file alone, `license-file = "LICENSE"`.
+[quantizr]
+clarify = { license = "MIT", files = [
+    { path = "LICENSE", checksum = "407b2d167f73ef78da1fcbfb6c2f1051f195b1984b9bfeeac0a39b34c198a7fe" },
+] }
+
+# Notices under a name or in a form the scan does not take.
+[libm]
+clarify = { license = "MIT", files = [
+    { path = "LICENSE.txt", checksum = "3823dda7cf046602f4b4e77ec8e227863dc4736037cc85bb33d9f19febe16bb7" },
+] }
+[brotli-decompressor]
+clarify = { license = "BSD-3-Clause", files = [
+    { path = "LICENSE", checksum = "c0c56f26d9c051cac4d200c34c84e7ae9aaa853e01a982a1df08b09931e518ae" },
+] }
+[exr]
+clarify = { license = "BSD-3-Clause", files = [
+    { path = "LICENSE.md", checksum = "97e4d3aa7a9e8ac31979c16ca8bb2b628a9cb72c3362185ad2bf4ad77f43551f" },
+] }
+[tsify]
+clarify = { license = "MIT OR Apache-2.0", files = [
+    { path = "LICENSE_MIT", license = "MIT", checksum = "23b988ff99c59aba4e37e7709d3d2102096203bb83a077cbc1aad04dd7a77244" },
+    { path = "LICENSE_APACHE", license = "Apache-2.0", checksum = "62c7a1e35f56406896d7aa7ca52d0cc0d272ac022b5d2796e7d6905db8a3636a" },
+] }
+
+# Crates published without their notice, read from the repository.
+[tsify-macros]
+clarify = { license = "MIT", git = [
+    { path = "LICENSE_MIT", checksum = "23b988ff99c59aba4e37e7709d3d2102096203bb83a077cbc1aad04dd7a77244" },
+] }
+[archmage-macros]
+clarify = { license = "MIT", git = [
+    { path = "LICENSE-MIT", checksum = "ea17bff5189bc1a38dcad7bd93abeb5a348da5ebeee5891a012b5db27a2a084b" },
+] }
+[magetypes]
+clarify = { license = "MIT", git = [
+    { path = "LICENSE-MIT", checksum = "ea17bff5189bc1a38dcad7bd93abeb5a348da5ebeee5891a012b5db27a2a084b" },
+] }
+[enough]
+clarify = { license = "MIT", git = [
+    { path = "LICENSE-MIT", checksum = "ffa509f359743823fe3cdba2c4dc8feee00be8f07ab299fbbe2b5a50d6ed1ecf" },
+] }
+[atomig-macro]
+clarify = { license = "MIT", git = [
+    { path = "LICENSE-MIT", checksum = "6f54826bbf67526f2d41937c1904ae2de63ef5707b80c68deadbf073b5669c40" },
+] }
+[profiling]
+clarify = { license = "MIT", git = [
+    { path = "LICENSE-MIT", checksum = "c8167fdeeed46d3f244d3f85c5bf998ce889343691c32be2c61a8bc4b5c08333" },
+] }
+[profiling-procmacros]
+clarify = { license = "MIT", git = [
+    { path = "LICENSE-MIT", checksum = "c8167fdeeed46d3f244d3f85c5bf998ce889343691c32be2c61a8bc4b5c08333" },
+] }
+[pulp-wasm-simd-flag]
+clarify = { license = "MIT", git = [
+    { path = "LICENSE", checksum = "d64f878c89bd5f1e5ada7e4aad57690b122727cf5229b7b87ea1980c188da1d9" },
+] }
+[alloc-stdlib]
+clarify = { license = "BSD-3-Clause", git = [
+    { path = "LICENSE", checksum = "c0c56f26d9c051cac4d200c34c84e7ae9aaa853e01a982a1df08b09931e518ae" },
+] }
+[fast-ssim2]
+clarify = { license = "BSD-2-Clause", git = [
+    { path = "LICENSE", checksum = "acc9e236b0011c638714a16f5634fa5bcd3be111182e237c3049db700c3521e2" },
+] }
diff --git a/crates/sqzer-wasm/README.md b/crates/sqzer-wasm/README.md
index 4a2941b..eaf7a8c 100644
--- a/crates/sqzer-wasm/README.md
+++ b/crates/sqzer-wasm/README.md
@@ -146,4 +146,4 @@ await init({ module_or_path: await readFile(new URL(import.meta.resolve("sqzer/s
 
 ## Licence
 
-MIT or Apache-2.0, at your option.
+MIT or Apache-2.0, at your option. `THIRD-PARTY-LICENSES.txt` in the package carries the notice of every crate compiled into `sqzer_bg.wasm`, the C library inside `libdeflate-sys` included; a page that bundles the package ships it alongside, as most of those licences ask.
diff --git a/crates/sqzer-wasm/about.hbs b/crates/sqzer-wasm/about.hbs
new file mode 100644
index 0000000..2ff059f
--- /dev/null
+++ b/crates/sqzer-wasm/about.hbs
@@ -0,0 +1,22 @@
+Third-party notices for the npm package sqzer
+
+The package itself is MIT OR Apache-2.0, in LICENSE-MIT and LICENSE-APACHE
+next to this file. sqzer_bg.wasm is compiled from the crates below, each
+under the licence named, with the notice the crate ships, or the one its
+repository holds where the crate ships none. A crate under MPL-2.0 has its
+source at the repository given with it.
+
+{{#each licenses}}
+{{#unless (eq used_by.0.crate.repository "https://github.com/sqzer-dev/sqzer")}}
+================================================================================
+{{{name}}}
+
+Used by:
+{{#each used_by}}
+  {{{crate.name}}} {{{crate.version}}}{{#if crate.repository}}  {{{crate.repository}}}{{/if}}
+{{/each}}
+
+{{{text}}}
+
+{{/unless}}
+{{/each}}
diff --git a/crates/sqzer-wasm/pack.sh b/crates/sqzer-wasm/pack.sh
index e385555..e7af69b 100755
--- a/crates/sqzer-wasm/pack.sh
+++ b/crates/sqzer-wasm/pack.sh
@@ -4,7 +4,7 @@
 # (ADR-0011 D5), and what the wasm job of `ci.yml` rehearses on every pull
 # request. Leaves `pkg/sqzer-<version>.tgz`.
 #
-# Needs `wasm-pack`, `clang`, `jq` and Node 22.14 or later.
+# Needs `wasm-pack`, `cargo-about`, `clang`, `jq` and Node 22.14 or later.
 set -euo pipefail
 cd "$(dirname "$0")"
 
@@ -19,7 +19,25 @@ env -u RUSTFLAGS wasm-pack build --release --target web --out-name sqzer
 # the licence texts in the crate directory; they are at the repository
 # root.
 cp ../../LICENSE-MIT ../../LICENSE-APACHE pkg/
-jq '.name = "sqzer" | .files += ["snippets", "LICENSE-MIT", "LICENSE-APACHE"]' \
+
+# The notices of every crate compiled into the module, from `about.toml`
+# at the repository root and `about.hbs` here. Most of their licences ask
+# that the copyright notice travels with a binary; this is where it
+# travels. `--fail` refuses a crate whose licence cannot be read. A stale
+# clarification in `about.toml`, a crate whose licence file moved with a
+# bump, is only a warning to `cargo about`, which then drops that notice
+# and goes on; here a warning fails the build, so nothing is left out
+# without anyone knowing.
+about_log=$(cargo about generate --fail --locked --target wasm32-unknown-unknown \
+  -o pkg/THIRD-PARTY-LICENSES.txt about.hbs 2>&1) || { echo "$about_log" >&2; exit 1; }
+if grep -q WARN <<< "$about_log"; then
+  echo "$about_log" >&2
+  echo "cargo about warned: a notice is missing, or a clarification in about.toml is stale" >&2
+  exit 1
+fi
+test -s pkg/THIRD-PARTY-LICENSES.txt
+
+jq '.name = "sqzer" | .files += ["snippets", "LICENSE-MIT", "LICENSE-APACHE", "THIRD-PARTY-LICENSES.txt"]' \
   pkg/package.json > pkg/package.json.new
 mv pkg/package.json.new pkg/package.json
 
diff --git a/crates/sqzer-wasm/tests/package.mjs b/crates/sqzer-wasm/tests/package.mjs
index d232ed7..822e8fa 100644
--- a/crates/sqzer-wasm/tests/package.mjs
+++ b/crates/sqzer-wasm/tests/package.mjs
@@ -17,6 +17,12 @@ assert.equal(manifest.license, "MIT OR Apache-2.0");
 for (const file of ["LICENSE-MIT", "LICENSE-APACHE", "README.md", "sqzer.d.ts"]) {
   await readFile(installed(file));
 }
+// The notices of the crates in the module, one `Used by` block per
+// licence text, with the C library inside `libdeflate-sys` among them.
+const notices = await readFile(installed("THIRD-PARTY-LICENSES.txt"), "utf8");
+for (const needle of ["Used by:", "ravif", "mozjpeg-rs", "libdeflate-sys", "Eric Biggers", "avif-parse"]) {
+  assert.ok(notices.includes(needle), `THIRD-PARTY-LICENSES.txt lacks ${needle}`);
+}
 
 await init({ module_or_path: await readFile(installed("sqzer_bg.wasm")) });