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

scripts/gen_surface_types.py

@@ -55,6 +55,18 @@ SCHEMA_PATCHES: dict[str, list[tuple[str, Any, Any]]] = {
             {"$ref": "#/$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"]),

src/mcp-types/mcp_types/_v2025_11_25/__init__.py

@@ -1358,7 +1358,7 @@ class InputSchema(WireModel):
         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"]
 
@@ -1376,7 +1376,7 @@ class OutputSchema(WireModel):
         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"]
 

tests/types/test_methods.py

@@ -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)