fix(server): omit derived tool schema titles

Author: daleselaji-dev

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

@@ -21,7 +21,7 @@
     returns_input_required,
 )
 from mcp.server.mcpserver.utilities.context_injection import find_context_parameter
-from mcp.server.mcpserver.utilities.func_metadata import FuncMetadata, func_metadata
+from mcp.server.mcpserver.utilities.func_metadata import FuncMetadata, NoTitleJsonSchema, func_metadata
 from mcp.shared._callable_inspection import is_async_callable
 from mcp.shared.exceptions import MCPError
 from mcp.shared.tool_name_validation import validate_and_warn_tool_name
@@ -103,7 +103,7 @@ def from_function(
             skip_names=skip_names,
             structured_output=structured_output,
         )
-        parameters = func_arg_metadata.arg_model.model_json_schema(by_alias=True)
+        parameters = func_arg_metadata.arg_model.model_json_schema(by_alias=True, schema_generator=NoTitleJsonSchema)
 
         # Match `model_dump_one_level`'s kwarg keys (alias when present, else field name)
         # so a by-name resolver param resolves to a key that exists at call time.

src/mcp/server/mcpserver/utilities/func_metadata.py

@@ -74,6 +74,14 @@ def emit_warning(self, kind: JsonSchemaWarningKind, detail: str) -> None:
         raise ValueError(f"JSON schema warning: {kind} - {detail}")
 
 
+class NoTitleJsonSchema(StrictJsonSchema):
+    """A strict JSON schema generator that omits titles derived from field names."""
+
+    def field_title_should_be_set(self, schema: Any) -> bool:
+        """Return false so Pydantic does not add a title derived from the field name."""
+        return False
+
+
 _LOCAL_DEFS_PREFIX = "#/$defs/"
 
 

tests/server/mcpserver/test_title.py

@@ -1,7 +1,10 @@
 """Integration tests for title field functionality."""
 
+from typing import Annotated
+
 import pytest
 from mcp_types import Prompt, Resource, ResourceTemplate, Tool, ToolAnnotations
+from pydantic import Field
 
 from mcp import Client
 from mcp.server.mcpserver import MCPServer
@@ -87,6 +90,23 @@ def tool_with_both(message: str) -> str:  # pragma: no cover
         assert both.title == "Primary Title"
 
 
+@pytest.mark.anyio
+async def test_tool_input_schema_omits_derived_titles_but_preserves_explicit_titles():
+    """Tool schemas omit Pydantic's field-name titles while preserving explicit titles."""
+    mcp = MCPServer(name="SchemaTitleServer")
+
+    @mcp.tool()
+    def typed_tool(required: str, explicit: Annotated[int, Field(title="Explicit Count")]) -> str:  # pragma: no cover
+        return f"{required}: {explicit}"
+
+    async with Client(mcp) as client:
+        tools = await client.list_tools()
+
+    properties = tools.tools[0].input_schema["properties"]
+    assert properties["required"] == {"type": "string"}
+    assert properties["explicit"] == {"title": "Explicit Count", "type": "integer"}
+
+
 @pytest.mark.anyio
 async def test_prompt_title():
     """Test that prompt titles work correctly."""