feat(tools): inline local $ref in tool inputSchema (#2384)#2448
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MukundaKatta wants to merge 3 commits intomodelcontextprotocol:mainfrom
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feat(tools): inline local $ref in tool inputSchema (#2384)#2448MukundaKatta wants to merge 3 commits intomodelcontextprotocol:mainfrom
MukundaKatta wants to merge 3 commits intomodelcontextprotocol:mainfrom
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…textprotocol#2384) Pydantic's model_json_schema() emits $ref/$defs for nested models, but LLM clients consuming tools/list often cannot resolve $ref and serialize referenced parameters as stringified JSON instead of structured objects. Inline local $ref pointers in tool schemas so they're self-contained and LLM-consumable, matching behavior in typescript-sdk (modelcontextprotocol#1563) and go-sdk. Behavior: - Caches resolved defs (diamond references resolve each def once) - Cycles left in place with $defs entries preserved (degraded but correct) - Sibling keywords alongside $ref preserved per JSON Schema 2020-12 - External $ref and unknown local refs untouched - Input schema not mutated Changes: - Add mcp/server/mcpserver/utilities/schema.py with dereference_local_refs() - Apply to tool inputSchema at Tool.from_function() - 11 unit tests covering simple refs, diamond, cycles, siblings, legacy 'definitions' keyword, external refs, unknown refs, nested arrays/objects, input immutability Closes modelcontextprotocol#2384 Signed-off-by: Mukunda Katta <mukunda.vjcs6@gmail.com>
…delcontextprotocol#2384) After the dereference_local_refs fix, the UserInput model's properties land directly under tool.parameters["properties"]["user"]["properties"] instead of inside the $defs container. Update the test assertions to match the new (LLM-consumable) schema shape. This is the only test in test_tool_manager.py that was checking the $defs location; all other tests check tool behavior or per-property fields that are unaffected by the inlining. Signed-off-by: Mukunda Katta <mukunda.vjcs6@gmail.com>
CI was failing on two checks (not test failures — earlier diagnostic was wrong):
1. pre-commit / Ruff Format — base.py had a multi-line wrap ruff wanted single-line.
2. Coverage check — project requires 100% coverage; schema.py was at 92.86%
with 3 uncovered lines (empty/null $defs short-circuits + a defensive
non-dict branch).
Changes:
- Apply ruff format to base.py.
- Mark the defensive non-dict branch in inline() with '# pragma: no cover'
with comment explaining it's only reachable for non-JSON-shaped values.
- Add 3 tests covering the previously-uncovered branches:
* empty $defs container ('{}')
* null $defs ('None')
* refs nested inside a list (anyOf array)
Local verification: 349 server tests pass, dereference_local_refs at 100%
coverage (14 tests), ruff check clean, ruff format clean.
Signed-off-by: Mukunda Katta <mukunda.vjcs6@gmail.com>
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Why
Pydantic's `model_json_schema()` emits `$ref`/`$defs` for nested models.
LLM clients consuming `tools/list` often cannot resolve `$ref` — they
serialize referenced parameters as stringified JSON instead of structured
objects. (See e.g. the Notion MCP server case in
anthropics/claude-code#18260.)
typescript-sdk addressed this in
modelcontextprotocol/typescript-sdk#1563
by inlining local `$ref` pointers. This PR adds the Python equivalent
so all SDKs emit LLM-consumable schemas.
What
`dereference_local_refs(schema)` that inlines `$ref` pointers to local
`#/$defs/...` (and legacy `#/definitions/...`).
Behavior
Tests
11 new unit tests in `tests/server/mcpserver/utilities/test_schema.py`
covering each of the cases above. Existing `tools/` tests continue to pass.
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