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Accept boolean sub-schemas in 2025-11-25 tool schema properties #3354

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Accept boolean sub-schemas in 2025-11-25 tool schema properties #3354

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12 changes: 12 additions & 0 deletions scripts/gen_surface_types.py
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Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,18 @@
{"$ref": "#/$defs/PrimitiveSchemaDefinition"},
{},
),
# JSON Schema 2020-12 allows a boolean wherever a sub-schema is expected, and
# 2026-07-28 already leaves these free-form; accept `true`/`false` property schemas.
(
"$defs/Tool/properties/inputSchema/properties/properties/additionalProperties",
{"additionalProperties": True, "properties": {}, "type": "object"},
{"anyOf": [{"additionalProperties": True, "properties": {}, "type": "object"}, {"type": "boolean"}]},
),
(
"$defs/Tool/properties/outputSchema/properties/properties/additionalProperties",
{"additionalProperties": True, "properties": {}, "type": "object"},
{"anyOf": [{"additionalProperties": True, "properties": {}, "type": "object"}, {"type": "boolean"}]},
),
],
"2026-07-28": [
("$defs/NumberSchema/properties/default/type", "number", ["integer", "number"]),
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4 changes: 2 additions & 2 deletions src/mcp-types/mcp_types/_v2025_11_25/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1358,7 +1358,7 @@
extra="allow",
)
schema_: Annotated[str | None, Field(alias="$schema")] = None
properties: dict[str, dict[str, Any]] | None = None
properties: dict[str, dict[str, Any] | bool] | None = None

Check warning on line 1361 in src/mcp-types/mcp_types/_v2025_11_25/__init__.py

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Claude / Claude Code Review

nit: `dict[str, Any] | bool` under pydantic smart union lax-coerces bool-ish scalars (1, 0, "true", "yes", "on", 1.0) into booleans, silently rewriting invalid property sub-schemas instead of rejecting them (same union at line 1379 in OutputSchema; WireMo 

nit: `dict[str, Any] | bool` under pydantic smart union lax-coerces bool-ish scalars (1, 0, "true", "yes", "on", 1.0) into booleans, silently rewriting invalid property sub-schemas instead of rejecting them (same union at line 1379 in OutputSchema; WireModel is not strict-mode)

@cubic-dev-ai cubic-dev-ai Bot Aug 21, 2026

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P2: When a properties value is "false" or 0, Pydantic's non-strict bool arm coerces it and accepts an invalid JSON Schema sub-schema. Generate this union with a strict boolean type, such as StrictBool or a strict boolean literal, in both schemas so only true and false are admitted.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At src/mcp-types/mcp_types/_v2025_11_25/__init__.py, line 1361:

<comment>When a `properties` value is `"false"` or `0`, Pydantic's non-strict `bool` arm coerces it and accepts an invalid JSON Schema sub-schema. Generate this union with a strict boolean type, such as `StrictBool` or a strict boolean literal, in both schemas so only `true` and `false` are admitted.</comment>

<file context>
@@ -1358,7 +1358,7 @@ class InputSchema(WireModel):
     )
     schema_: Annotated[str | None, Field(alias="$schema")] = None
-    properties: dict[str, dict[str, Any]] | None = None
+    properties: dict[str, dict[str, Any] | bool] | None = None
     required: list[str] | None = None
     type: Literal["object"]
</file context>

@claude claude Bot Aug 21, 2026

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🟡 nit: dict[str, Any] | bool under pydantic smart union lax-coerces bool-ish scalars (1, 0, "true", "yes", "on", 1.0) into booleans, silently rewriting invalid property sub-schemas instead of rejecting them (same union at line 1379 in OutputSchema; WireModel is not strict-mode)

Extended reasoning...

On a 2025-11-25 (or earlier legacy) session, a server advertises an invalid tool schema like "properties": {"flag": "true"} or {"flag": 1}. Before this change the ListToolsResult failed validation with a clear dict_type error; after it, the sieve silently coerces the value to boolean true, so the client (or a server forwarding a third-party schema) sees a mutated schema the peer never sent — contradicting the PR's claim that string/scalar property values are still rejected. Fix would be a strict-bool annotation on the bool arm of both unions (via the generator patch).

Verification: nit. The coercion path is real and unguarded. The new field is a plain smart union — properties: dict[str, dict[str, Any] | bool] | None = None at src/mcp-types/mcp_types/_v2025_11_25/init.py:1361 (InputSchema) and :1379 (OutputSchema) — with no strict annotation on the bool member. Nothing in the validation path enables strict mode: `WireModel.model_config = ConfigDict(populate_by_name=True

required: list[str] | None = None
type: Literal["object"]

Expand All @@ -1376,7 +1376,7 @@
extra="allow",
)
schema_: Annotated[str | None, Field(alias="$schema")] = None
properties: dict[str, dict[str, Any]] | None = None
properties: dict[str, dict[str, Any] | bool] | None = None
required: list[str] | None = None
type: Literal["object"]

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16 changes: 16 additions & 0 deletions tests/types/test_methods.py
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Original file line number Diff line number Diff line change
Expand Up @@ -474,6 +474,22 @@ def test_elicit_request_surface_accepts_loose_property_schemas():
assert isinstance(parsed, types.ElicitRequest)


def test_2025_11_25_tool_schema_surfaces_accept_boolean_sub_schemas():
"""JSON Schema 2020-12 allows `true`/`false` wherever a sub-schema is expected; real servers emit them."""
tool = {
"name": "echo",
"inputSchema": {"type": "object", "properties": {"arg": True}},
"outputSchema": {
"type": "object",
"properties": {"result": True, "hidden": False, "rows": {"type": "array", "items": True}},
"required": ["result"],
},
}
sieved = methods.serialize_server_result("tools/list", "2025-11-25", {"tools": [tool]})
assert sieved["tools"][0]["inputSchema"] == tool["inputSchema"]
assert sieved["tools"][0]["outputSchema"] == tool["outputSchema"]


def test_response_map_keys_mirror_the_request_map_keys():
assert set(methods.SERVER_RESULTS) == set(methods.CLIENT_REQUESTS)
assert set(methods.CLIENT_RESULTS) == set(methods.SERVER_REQUESTS)
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