GeezerVison

Trigger: a function with an unannotated parameter (def f(city): ..., or a lambda) registered as a resource template or prompt, or any caller of func_metadata(fn).arg_model.model_json_schema(). On the base, func_metadata.py:354 attached WithJsonSchema({"title": param.name, "type": "string"}), so the property was {"title": "city", "type": "string"}. Now it attaches {"type": "string"} and the default pydantic generator fills in a derived title. The diff's own test updates show the result: tests/server/mcpserver/test_func_metadata.py:314-315 go from "title": "x" to "title": "X". ResourceTemplate.parameters (resources/templates.py:116) is built at templates.py:156 with no schema_generator, so its stored schema changes value instead of losing the title. The PR text says this title is dropped; that holds only for tools. No guard applies: the field itself is public output.

Verification: Triggered when a function with an unannotated parameter is registered as a resource template. src/mcp/server/mcpserver/utilities/func_metadata.py:354 now attaches WithJsonSchema({"type": "string"}). Only src/mcp/server/mcpserver/tools/base.py:107 passes schema_generator=UntitledJsonSchema. So outside tools the title is replaced by a title-cased one, not dropped.

Condition: a caller outside this repo uses mcp.server.mcpserver.utilities.func_metadata.StrictJsonSchema directly, e.g. Model.model_json_schema(schema_generator=StrictJsonSchema), or subclasses it. Such callers cannot be enumerated from this checkout; the only in-repo use is…

Verification: Triggers when code outside this repo passes or subclasses StrictJsonSchema directly. Base: class StrictJsonSchema(GenerateJsonSchema) overrode only emit_warning. Head, src/mcp/server/mcpserver/utilities/func_metadata.py:76: class StrictJsonSchema(UntitledJsonSchema), so it now also drops every field-name-derived title. The docstring (lines 77-80) is unchanged.

Trigger: a tool declared -> Annotated[dict[str, float], Field(title="Temperatures", description="By city")], registered through Tool.from_function (src/mcp/server/mcpserver/tools/base.py:102), which calls func_metadata and then _create_output_model (func_metadata.py:457). inspect_annotation(...).type at func_metadata.py:390 strips Annotated, and line 524 sets model = type_expr. The schema derived at func_metadata.py:140 is {"additionalProperties": {"type": "number"}, "type": "object"} with neither the title nor the description. The base lost the same metadata: it wrapped type_expr in Field(title=f"{func_name}DictOutput"), so this is not a regression, and the TODO at func_metadata.py:522-523 names the loss. The wrapped path passes original_annotation to _create_wrapped_model (func_metadata.py:531), which is why Field metadata survives there. No safeguard applies: the new test at tests/server/mcpserver/test_tool_manager.py:910 only checks a BaseModel return.

Verification: pre-existing: triggers when a tool's return annotation is Annotated[dict[str, T], Field(title=..., description=...)]. For dict[str, T] (src/mcp/server/mcpserver/utilities/func_metadata.py lines 519-524) the model is model = type_expr, so the Field(...) metadata held only in original_annotation is discarded. The base line was model = Annotated[type_expr, Field(title=f"{func_name}DictOutput")], also built from the stripped type_expr.

There is no runtime trigger; this is a convention check on a test the diff adds. test_tool_schemas_keep_only_titles_set_explicitly at tests/server/mcpserver/test_tool_manager.py:910 goes straight from the def line to class Book(BaseModel): at line 911. .claude/skills/test-quality/SKILL.md:16-19 says "Docstrings: 1-2 sentences of behaviour, honest about provenance" and calls provenance "the triage key when the test later fails". The base branch does not have this test, so the gap is new. The same guide (SKILL.md:106-107) asks that registered-but-never-invoked bodies be raise NotImplementedError; find_book at line 915 uses .... No safeguard enforces either rule: ruff selects only D212 from pydocstyle (pyproject.toml:214).

Verification: tests/server/mcpserver/test_tool_manager.py:910-911 is added by this diff and goes straight from def test_tool_schemas_keep_only_titles_set_explicitly(): to class Book(BaseModel): with no docstring. The test pins SDK-defined schema output and does not say so. Nothing breaks: the test passes and its name already describes the behaviour.

Nothing fails at runtime, and validation is unaffected because title is an annotation keyword. What the instruction guards is the 2.x compatibility contract: after this change every MCPServer tool's tools/list entry loses the <func>Arguments root title, the <func>Output root title of wrapped results, the <func>DictOutput title of dict[str, X] results, the parameter-name title of unannotated parameters, and all field-name-derived property titles. It bites for a 2.x user who upgrades and has a client or UI that displays or keys on those titles, a snapshot test of their own tool schemas, or code that relies on output_schema == Model.model_json_schema() (the diff itself had to rewrite test_basemodel_union_input_required_result_derives_model_schema because that equality no longer holds). Two importable classes also change behaviour: StrictJsonSchema now suppresses field titles for anyone using it directly, and FuncMetadata.output_model for dict[str, X] is the bare type rather than Annotated[..., Field(title=...)].

Verification: Instruction: AGENTS.md (base 86ca12b), "Branching Model", second bullet, present as quoted: "v2 is released; its public API is a compatibility contract for the 2.x line. Removals, renames, or any change to an existing API's signature or observable behaviour (including ones softened by a @ deprecated shim) is a design decision a maintainer makes explicitly, and should generally be avoided." It binds library code under src/.

Nothing fails at runtime and pyright still passes, since it infers the return type. The instruction guards consistent, fully annotated code; it bites only as a convention gap on the one function this diff adds. Sized honestly: this is small, and every other test in tests/server/mcpserver/test_tool_manager.py and tests/server/mcpserver/tools/test_base.py also omits -> None, while the tests under tests/docs_src/ include it. The nested helper find_book and the new UntitledJsonSchema.field_title_should_be_set in src/ are fully annotated.

Verification: Instruction: AGENTS.md at base 86ca12b, section "## Code Quality", reads verbatim "- Type hints required for all code"; it is repo-root scoped and has no carve-out for tests. Code: tests/server/mcpserver/test_tool_manager.py:910, added by this diff, is def test_tool_schemas_keep_only_titles_set_explicitly(): with no return annotation. The function takes no parameters, so it carries no type hint at all. For the maintainer: nothing fails at runtime and pyright infers the return type.