Drop pydantic's auto-derived field titles from tool input schemas

src/mcp/server/mcpserver/tools/base.py

@@ -21,7 +21,7 @@
     returns_input_required,
 )
 from mcp.server.mcpserver.utilities.context_injection import find_context_parameter
-from mcp.server.mcpserver.utilities.func_metadata import FuncMetadata, func_metadata
+from mcp.server.mcpserver.utilities.func_metadata import FuncMetadata, NoAutoTitleJsonSchema, func_metadata
 from mcp.shared._callable_inspection import is_async_callable
 from mcp.shared.exceptions import MCPError
 from mcp.shared.tool_name_validation import validate_and_warn_tool_name
@@ -103,7 +103,9 @@ def from_function(
             skip_names=skip_names,
             structured_output=structured_output,
         )
-        parameters = func_arg_metadata.arg_model.model_json_schema(by_alias=True)
+        parameters = func_arg_metadata.arg_model.model_json_schema(
+            by_alias=True, schema_generator=NoAutoTitleJsonSchema
+        )
 
         # Match `model_dump_one_level`'s kwarg keys (alias when present, else field name)
         # so a by-name resolver param resolves to a key that exists at call time.

src/mcp/server/mcpserver/utilities/func_metadata.py

@@ -74,6 +74,22 @@ def emit_warning(self, kind: JsonSchemaWarningKind, detail: str) -> None:
         raise ValueError(f"JSON schema warning: {kind} - {detail}")
 
 
+class NoAutoTitleJsonSchema(GenerateJsonSchema):
+    """A JSON schema generator that omits pydantic's auto-derived field titles.
+
+    Pydantic titles every field by title-casing its name, so ``exercise_id``
+    gains ``"title": "Exercise Id"`` - a restatement of the key it sits under.
+    Tool schemas are sent to a model on every request, where that repetition is
+    paid for in context and carries nothing the field name does not.
+
+    Titles set explicitly via ``Field(title=...)`` are untouched: this only
+    suppresses the automatic ones.
+    """
+
+    def field_title_should_be_set(self, schema: Any) -> bool:
+        return False
+
+
 _LOCAL_DEFS_PREFIX = "#/$defs/"
 
 

tests/client/test_client.py

@@ -159,7 +159,7 @@ async def test_client_list_tools(app: MCPServer):
                         name="greet",
                         description="Greet someone by name.",
                         input_schema={
-                            "properties": {"name": {"title": "Name", "type": "string"}},
+                            "properties": {"name": {"type": "string"}},
                             "required": ["name"],
                             "title": "greetArguments",
                             "type": "object",

tests/docs_src/test_client.py

@@ -56,8 +56,8 @@ async def test_list_tools_returns_the_full_definition() -> None:
             {
                 "type": "object",
                 "properties": {
-                    "query": {"title": "Query", "type": "string"},
-                    "limit": {"default": 10, "title": "Limit", "type": "integer"},
+                    "query": {"type": "string"},
+                    "limit": {"default": 10, "type": "integer"},
                 },
                 "required": ["query"],
                 "title": "search_booksArguments",

tests/docs_src/test_context.py

@@ -20,7 +20,7 @@ async def test_the_context_parameter_is_not_in_the_input_schema() -> None:
         assert tool.input_schema == snapshot(
             {
                 "type": "object",
-                "properties": {"query": {"title": "Query", "type": "string"}},
+                "properties": {"query": {"type": "string"}},
                 "required": ["query"],
                 "title": "search_booksArguments",
             }

tests/docs_src/test_dependencies.py

@@ -31,7 +31,7 @@ async def test_the_resolved_parameter_is_invisible_to_the_model() -> None:
     assert tool.input_schema == snapshot(
         {
             "type": "object",
-            "properties": {"title": {"title": "Title", "type": "string"}},
+            "properties": {"title": {"type": "string"}},
             "required": ["title"],
             "title": "reserve_bookArguments",
         }

tests/docs_src/test_first_steps.py

@@ -27,8 +27,8 @@ async def test_each_decorator_registers_one_primitive() -> None:
             {
                 "type": "object",
                 "properties": {
-                    "a": {"title": "A", "type": "integer"},
-                    "b": {"title": "B", "type": "integer"},
+                    "a": {"type": "integer"},
+                    "b": {"type": "integer"},
                 },
                 "required": ["a", "b"],
                 "title": "addArguments",

tests/docs_src/test_lifespan.py

@@ -29,7 +29,7 @@ async def test_context_parameter_never_reaches_the_input_schema() -> None:
         assert tool.input_schema == snapshot(
             {
                 "type": "object",
-                "properties": {"genre": {"title": "Genre", "type": "string"}},
+                "properties": {"genre": {"type": "string"}},
                 "required": ["genre"],
                 "title": "count_booksArguments",
             }

tests/docs_src/test_progress.py

@@ -19,9 +19,7 @@ async def test_context_parameter_is_invisible_to_the_model() -> None:
     """tutorial001: `ctx` comes from the type hint and never reaches the input schema."""
     async with Client(tutorial001.mcp) as client:
         (tool,) = (await client.list_tools()).tools
-        assert tool.input_schema["properties"] == {
-            "urls": {"items": {"type": "string"}, "title": "Urls", "type": "array"}
-        }
+        assert tool.input_schema["properties"] == {"urls": {"items": {"type": "string"}, "type": "array"}}
         assert tool.input_schema["required"] == ["urls"]
 
 

tests/docs_src/test_real_host.py

@@ -20,7 +20,7 @@ async def test_the_host_sees_exactly_what_the_decorators_registered() -> None:
         assert search.input_schema == snapshot(
             {
                 "type": "object",
-                "properties": {"query": {"title": "Query", "type": "string"}},
+                "properties": {"query": {"type": "string"}},
                 "required": ["query"],
                 "title": "search_booksArguments",
             }

tests/docs_src/test_tools.py

@@ -21,8 +21,8 @@ async def test_signature_becomes_the_schema() -> None:
             {
                 "type": "object",
                 "properties": {
-                    "query": {"title": "Query", "type": "string"},
-                    "limit": {"title": "Limit", "type": "integer"},
+                    "query": {"type": "string"},
+                    "limit": {"type": "integer"},
                 },
                 "required": ["query", "limit"],
                 "title": "search_booksArguments",
@@ -50,8 +50,8 @@ async def test_default_value_makes_the_argument_optional() -> None:
             {
                 "type": "object",
                 "properties": {
-                    "query": {"title": "Query", "type": "string"},
-                    "limit": {"default": 10, "title": "Limit", "type": "integer"},
+                    "query": {"type": "string"},
+                    "limit": {"default": 10, "type": "integer"},
                 },
                 "required": ["query"],
                 "title": "search_booksArguments",
@@ -73,7 +73,6 @@ async def test_field_constraints_land_in_the_schema() -> None:
                 "description": "Maximum number of results.",
                 "maximum": 50,
                 "minimum": 1,
-                "title": "Limit",
                 "type": "integer",
             }
         )

tests/server/mcpserver/test_resolve.py

@@ -2766,7 +2766,7 @@ async def quote(title: str, price: Annotated[int, Resolve(price_of)]) -> str:
     assert advertised.input_schema == snapshot(
         {
             "type": "object",
-            "properties": {"title": {"title": "Title", "type": "string"}},
+            "properties": {"title": {"type": "string"}},
             "required": ["title"],
             "title": "quoteArguments",
         }

tests/server/mcpserver/test_tool_manager.py

@@ -1,11 +1,11 @@
 import json
 import logging
 from dataclasses import dataclass
-from typing import Any, TypedDict
+from typing import Annotated, Any, TypedDict
 
 import pytest
 from mcp_types import CallToolResult, TextContent, ToolAnnotations
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 
 from mcp.server.context import LifespanContextT, RequestT
 from mcp.server.mcpserver import Context, MCPServer
@@ -904,3 +904,33 @@ def test_func() -> str:  # pragma: no cover
         # Remove with correct case
         manager.remove_tool("test_func")
         assert manager.get_tool("test_func") is None
+
+
+def test_tool_input_schema_omits_auto_derived_titles():
+    """Auto-derived field titles are dropped; explicit ones survive.
+
+    Pydantic titles every field by title-casing its name, which restates the key
+    it sits under. Tool schemas are sent to the model on every request, so that
+    repetition costs context for nothing.
+    """
+
+    def log_set(
+        exercise_id: str,
+        reps: Annotated[int, Field(title="Repetitions performed")],
+        weight: Annotated[float, Field(description="in kilograms")] = 0.0,
+    ) -> str:
+        """Log a set."""
+        return "ok"
+
+    manager = ToolManager()
+    tool = manager.add_tool(log_set)
+    properties = tool.parameters["properties"]
+
+    assert "title" not in properties["exercise_id"]
+    assert "title" not in properties["weight"]
+    # An explicitly-set title is the author's choice, not pydantic's default.
+    assert properties["reps"]["title"] == "Repetitions performed"
+    # Nothing else about the schema changes.
+    assert properties["exercise_id"]["type"] == "string"
+    assert properties["weight"]["description"] == "in kilograms"
+    assert properties["weight"]["default"] == 0.0