Merge pull request #626 from deepak-stratforge/feature/exclude-args-support

src/fastmcp/server/openapi.py

@@ -226,6 +226,7 @@ class OpenAPITool(Tool):
         tags: set[str] = set(),
         timeout: float | None = None,
         annotations: ToolAnnotations | None = None,
+        exclude_args: list[str] | None = None,
         serializer: Callable[[Any], str] | None = None,
     ):
         super().__init__(
@@ -235,6 +236,7 @@ class OpenAPITool(Tool):
             fn=self._execute_request,  # We'll use an instance method instead of a global function
             tags=tags,
             annotations=annotations,
+            exclude_args=exclude_args,
             serializer=serializer,
         )
         self._client = client

src/fastmcp/server/server.py

@@ -501,6 +501,7 @@ class FastMCP(Generic[LifespanResultT]):
         description: str | None = None,
         tags: set[str] | None = None,
         annotations: ToolAnnotations | dict[str, Any] | None = None,
+        exclude_args: list[str] | None = None,
     ) -> None:
         """Add a tool to the server.
 
@@ -523,6 +524,7 @@ class FastMCP(Generic[LifespanResultT]):
             description=description,
             tags=tags,
             annotations=annotations,
+            exclude_args=exclude_args,
         )
         self._cache.clear()
 
@@ -544,6 +546,7 @@ class FastMCP(Generic[LifespanResultT]):
         description: str | None = None,
         tags: set[str] | None = None,
         annotations: ToolAnnotations | dict[str, Any] | None = None,
+        exclude_args: list[str] | None = None,
     ) -> Callable[[AnyFunction], AnyFunction]:
         """Decorator to register a tool.
 
@@ -587,6 +590,7 @@ class FastMCP(Generic[LifespanResultT]):
                 description=description,
                 tags=tags,
                 annotations=annotations,
+                exclude_args=exclude_args,
             )
             return fn
 

src/fastmcp/tools/tool.py

@@ -46,6 +46,10 @@ class Tool(BaseModel):
     annotations: ToolAnnotations | None = Field(
         None, description="Additional annotations about the tool"
     )
+    exclude_args: list[str] | None = Field(
+        None,
+        description="Arguments to exclude from the tool schema, such as State, Memory, or Credential",
+    )
     serializer: Callable[[Any], str] | None = Field(
         None, description="Optional custom serializer for tool results"
     )
@@ -58,6 +62,7 @@ class Tool(BaseModel):
         description: str | None = None,
         tags: set[str] | None = None,
         annotations: ToolAnnotations | None = None,
+        exclude_args: list[str] | None = None,
         serializer: Callable[[Any], str] | None = None,
     ) -> Tool:
         """Create a Tool from a function."""
@@ -71,6 +76,18 @@ class Tool(BaseModel):
             if param.kind == inspect.Parameter.VAR_KEYWORD:
                 raise ValueError("Functions with **kwargs are not supported as tools")
 
+        if exclude_args:
+            for arg_name in exclude_args:
+                if arg_name not in sig.parameters:
+                    raise ValueError(
+                        f"Parameter '{arg_name}' in exclude_args does not exist in function."
+                    )
+                param = sig.parameters[arg_name]
+                if param.default == inspect.Parameter.empty:
+                    raise ValueError(
+                        f"Parameter '{arg_name}' in exclude_args must have a default value."
+                    )
+
         func_name = name or getattr(fn, "__name__", None) or fn.__class__.__name__
 
         if func_name == "<lambda>":
@@ -86,10 +103,14 @@ class Tool(BaseModel):
         schema = type_adapter.json_schema()
 
         context_kwarg = find_kwarg_by_type(fn, kwarg_type=Context)
+        temp_prune_params: list[str] = []
         if context_kwarg:
-            prune_params = [context_kwarg]
-        else:
-            prune_params = None
+            temp_prune_params.append(context_kwarg)
+        if exclude_args:
+            temp_prune_params.extend(exclude_args)
+        prune_params: list[str] | None = (
+            None if not temp_prune_params else temp_prune_params
+        )
 
         schema = compress_schema(schema, prune_params=prune_params)
 
@@ -100,6 +121,7 @@ class Tool(BaseModel):
             parameters=schema,
             tags=tags or set(),
             annotations=annotations,
+            exclude_args=exclude_args,
             serializer=serializer,
         )
 

src/fastmcp/tools/tool_manager.py

@@ -66,6 +66,7 @@ class ToolManager:
         description: str | None = None,
         tags: set[str] | None = None,
         annotations: ToolAnnotations | None = None,
+        exclude_args: list[str] | None = None,
     ) -> Tool:
         """Add a tool to the server."""
         tool = Tool.from_function(
@@ -75,6 +76,7 @@ class ToolManager:
             tags=tags,
             annotations=annotations,
             serializer=self._serializer,
+            exclude_args=exclude_args,
         )
         return self.add_tool(tool)
 

tests/server/test_tool_exclude_args.py

@@ -0,0 +1,92 @@
+from typing import Any
+
+import pytest
+from mcp.types import TextContent
+
+from fastmcp import Client, FastMCP
+
+
+async def test_tool_exclude_args_in_tool_manager():
+    """Test that tool args are excluded in the tool manager."""
+    mcp = FastMCP("Test Server")
+
+    @mcp.tool(exclude_args=["state"])
+    def echo(message: str, state: dict[str, Any] | None = None) -> str:
+        """Echo back the message provided."""
+        if state:
+            # State was read
+            pass
+        return message
+
+    tools = mcp._tool_manager.list_tools()
+    assert len(tools) == 1
+    assert tools[0].exclude_args is not None
+    for args in tools[0].exclude_args:
+        assert args not in tools[0].parameters
+
+
+async def test_tool_exclude_args_without_default_value_raises_error():
+    """Test that excluding args without default values raises ValueError"""
+    mcp = FastMCP("Test Server")
+
+    with pytest.raises(ValueError):
+
+        @mcp.tool(exclude_args=["state"])
+        def echo(message: str, state: dict[str, Any] | None) -> str:
+            """Echo back the message provided."""
+            if state:
+                # State was read
+                pass
+            return message
+
+
+async def test_add_tool_method_exclude_args():
+    """Test that tool exclude_args work with the add_tool method."""
+    mcp = FastMCP("Test Server")
+
+    def create_item(
+        name: str, value: int, state: dict[str, Any] | None = None
+    ) -> dict[str, Any]:
+        """Create a new item."""
+        if state:
+            # State was read
+            pass
+        return {"name": name, "value": value}
+
+    mcp.add_tool(create_item, name="create_item", exclude_args=["state"])
+
+    # Check internal tool objects directly
+    tools = mcp._tool_manager.list_tools()
+    assert len(tools) == 1
+    assert tools[0].exclude_args is not None
+    assert tools[0].exclude_args == ["state"]
+    for args in tools[0].exclude_args:
+        assert args not in tools[0].parameters
+
+
+async def test_tool_functionality_with_exclude_args():
+    """Test that tool functionality is preserved when using exclude_args."""
+    mcp = FastMCP("Test Server")
+
+    def create_item(
+        name: str, value: int, state: dict[str, Any] | None = None
+    ) -> dict[str, Any]:
+        """Create a new item."""
+        if state:
+            # state was read
+            pass
+        return {"name": name, "value": value}
+
+    mcp.add_tool(create_item, name="create_item", exclude_args=["state"])
+
+    # Use the tool to verify functionality is preserved
+    async with Client(mcp) as client:
+        result = await client.call_tool(
+            "create_item", {"name": "test_item", "value": 42}
+        )
+        assert len(result) == 1
+        assert isinstance(result[0], TextContent)
+
+        # The result should contain the expected JSON
+        assert '"name": "test_item"' in result[0].text
+        assert '"value": 42' in result[0].text