Revert "add output_schema override to support ChatGPT App SDK"

This reverts commit 88bc72d.

Author: mat-octave

src/mcp/server/fastmcp/server.py

@@ -385,7 +385,6 @@ def add_tool(
         annotations: ToolAnnotations | None = None,
         icons: list[Icon] | None = None,
         meta: dict[str, Any] | None = None,
-        output_schema: dict[str, Any] | None = None,
         structured_output: bool | None = None,
     ) -> None:
         """Add a tool to the server.
@@ -399,8 +398,6 @@ def add_tool(
             title: Optional human-readable title for the tool
             description: Optional description of what the tool does
             annotations: Optional ToolAnnotations providing additional tool information
-            meta: Optional metadata dictionary
-            output_schema: Optional Pydantic model defining the output schema separate from the tool's return type
             structured_output: Controls whether the tool's output is structured or unstructured
                 - If None, auto-detects based on the function's return type annotation
                 - If True, creates a structured tool (return type annotation permitting)
@@ -414,7 +411,6 @@ def add_tool(
             annotations=annotations,
             icons=icons,
             meta=meta,
-            output_schema=output_schema,
             structured_output=structured_output,
         )
 
@@ -437,7 +433,6 @@ def tool(
         annotations: ToolAnnotations | None = None,
         icons: list[Icon] | None = None,
         meta: dict[str, Any] | None = None,
-        output_schema: dict[str, Any] | None = None,
         structured_output: bool | None = None,
     ) -> Callable[[AnyFunction], AnyFunction]:
         """Decorator to register a tool.
@@ -451,8 +446,6 @@ def tool(
             title: Optional human-readable title for the tool
             description: Optional description of what the tool does
             annotations: Optional ToolAnnotations providing additional tool information
-            meta: Optional metadata dictionary
-            output_schema: Optional Pydantic model defining the output schema separate from the tool's return type
             structured_output: Controls whether the tool's output is structured or unstructured
                 - If None, auto-detects based on the function's return type annotation
                 - If True, creates a structured tool (return type annotation permitting)
@@ -488,7 +481,6 @@ def decorator(fn: AnyFunction) -> AnyFunction:
                 annotations=annotations,
                 icons=icons,
                 meta=meta,
-                output_schema=output_schema,
                 structured_output=structured_output,
             )
             return fn

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

@@ -35,15 +35,9 @@ class Tool(BaseModel):
     annotations: ToolAnnotations | None = Field(None, description="Optional annotations for the tool")
     icons: list[Icon] | None = Field(default=None, description="Optional list of icons for this tool")
     meta: dict[str, Any] | None = Field(default=None, description="Optional metadata for this tool")
-    output_schema_override: dict[str, Any] | None = Field(
-        default=None,
-        description="Optional Pydantic model defining the output schema separate from the tool's return type",
-    )
 
     @cached_property
     def output_schema(self) -> dict[str, Any] | None:
-        if self.output_schema_override is not None:
-            return self.output_schema_override
         return self.fn_metadata.output_schema
 
     @classmethod
@@ -57,7 +51,6 @@ def from_function(
         annotations: ToolAnnotations | None = None,
         icons: list[Icon] | None = None,
         meta: dict[str, Any] | None = None,
-        output_schema: dict[str, Any] | None = None,
         structured_output: bool | None = None,
     ) -> Tool:
         """Create a Tool from a function."""
@@ -91,7 +84,6 @@ def from_function(
             annotations=annotations,
             icons=icons,
             meta=meta,
-            output_schema_override=output_schema,
         )
 
     async def run(
@@ -106,7 +98,7 @@ async def run(
                 self.fn,
                 self.is_async,
                 arguments,
-                ({self.context_kwarg: context} if self.context_kwarg is not None else None),
+                {self.context_kwarg: context} if self.context_kwarg is not None else None,
             )
 
             if convert_result:

src/mcp/server/fastmcp/tools/tool_manager.py

@@ -51,7 +51,6 @@ def add_tool(
         annotations: ToolAnnotations | None = None,
         icons: list[Icon] | None = None,
         meta: dict[str, Any] | None = None,
-        output_schema: dict[str, Any] | None = None,
         structured_output: bool | None = None,
     ) -> Tool:
         """Add a tool to the server."""
@@ -63,7 +62,6 @@ def add_tool(
             annotations=annotations,
             icons=icons,
             meta=meta,
-            output_schema=output_schema,
             structured_output=structured_output,
         )
         existing = self._tools.get(tool.name)

tests/server/fastmcp/test_tool_manager.py

@@ -4,7 +4,7 @@
 from typing import Any, TypedDict
 
 import pytest
-from pydantic import BaseModel, Field
+from pydantic import BaseModel
 
 from mcp.server.fastmcp import Context, FastMCP
 from mcp.server.fastmcp.exceptions import ToolError
@@ -577,97 +577,13 @@ def get_user() -> UserOutput:
 
         # Test that output_schema is populated
         expected_schema = {
-            "properties": {
-                "name": {"type": "string", "title": "Name"},
-                "age": {"type": "integer", "title": "Age"},
-            },
+            "properties": {"name": {"type": "string", "title": "Name"}, "age": {"type": "integer", "title": "Age"}},
             "required": ["name", "age"],
             "title": "UserOutput",
             "type": "object",
         }
         assert tool.output_schema == expected_schema
 
-    def test_add_output_schema_override(self):
-        """Test registering a tool with an explicit output schema."""
-
-        # For the ChatGPT App SDK, the tool output should be structured like:
-        # {
-        #   "structuredOutput": { ... },
-        #   "content": [ { "type": "text", "text": "..." }, ... ],
-        #   "_meta": { ... }
-        # }
-        # and the tool output schema should reflect the structure of "structuredOutput"
-        class UserOutput(BaseModel):
-            name: str
-            age: int
-
-        # Output structure expected by ChatGPT App SDK
-        class ToolOutput(BaseModel):
-            structuredOutput: UserOutput
-            content: list[dict[str, str]]
-            meta: dict[str, Any] = Field(alias="_meta")
-
-        def get_user(user_id: int) -> ToolOutput:
-            """Get user by ID."""
-            return ToolOutput(
-                structuredOutput=UserOutput(name="John", age=30),
-                content=[{"type": "text", "text": "User found"}],
-                _meta={"request_id": "12345"},
-            )
-
-        manager = ToolManager()
-        tool = manager.add_tool(get_user, output_schema=UserOutput.model_json_schema())
-
-        expected_schema = {
-            "properties": {
-                "name": {"type": "string", "title": "Name"},
-                "age": {"type": "integer", "title": "Age"},
-            },
-            "required": ["name", "age"],
-            "title": "UserOutput",
-            "type": "object",
-        }
-        assert tool.output_schema == expected_schema
-        assert tool.fn_metadata.output_model == ToolOutput
-
-    @pytest.mark.anyio
-    async def test_call_tool_with_output_schema_override(self):
-        # For the ChatGPT App SDK, the tool output should be structured like:
-        # {
-        #   "structuredOutput": { ... },
-        #   "content": [ { "type": "text", "text": "..." }, ... ],
-        #   "_meta": { ... }
-        # }
-        # and the tool output schema should reflect the structure of "structuredOutput"
-        class UserOutput(BaseModel):
-            name: str
-            age: int
-
-        # Output structure expected by ChatGPT App SDK
-        class ToolOutput(BaseModel):
-            structuredOutput: UserOutput
-            content: list[dict[str, str]]
-            meta: dict[str, Any] = Field(alias="_meta")
-
-        def get_user(user_id: int) -> ToolOutput:
-            """Get user by ID."""
-            return ToolOutput(
-                structuredOutput=UserOutput(name="John", age=30),
-                content=[{"type": "some more information about the output data"}],
-                _meta={"request_id": "12345"},
-            )
-
-        manager = ToolManager()
-        manager.add_tool(get_user, output_schema=UserOutput.model_json_schema())
-        result = await manager.call_tool("get_user", {"user_id": 1}, convert_result=True)
-
-        expected_result = {
-            "structuredOutput": {"name": "John", "age": 30},
-            "content": [{"type": "some more information about the output data"}],
-            "_meta": {"request_id": "12345"},
-        }
-        assert len(result) == 2 and result[1] == expected_result
-
     @pytest.mark.anyio
     async def test_tool_with_dict_str_any_output(self):
         """Test tool with dict[str, Any] return type."""