Support enabled/disabled tools

src/fastmcp/server/server.py

@@ -625,6 +625,7 @@ class FastMCP(Generic[LifespanResultT]):
         tags: set[str] | None = None,
         annotations: ToolAnnotations | dict[str, Any] | None = None,
         exclude_args: list[str] | None = None,
+        enabled: bool | None = None,
     ) -> FunctionTool: ...
 
     @overload
@@ -637,6 +638,7 @@ class FastMCP(Generic[LifespanResultT]):
         tags: set[str] | None = None,
         annotations: ToolAnnotations | dict[str, Any] | None = None,
         exclude_args: list[str] | None = None,
+        enabled: bool | None = None,
     ) -> Callable[[AnyFunction], FunctionTool]: ...
 
     def tool(
@@ -648,6 +650,7 @@ class FastMCP(Generic[LifespanResultT]):
         tags: set[str] | None = None,
         annotations: ToolAnnotations | dict[str, Any] | None = None,
         exclude_args: list[str] | None = None,
+        enabled: bool | None = None,
     ) -> Callable[[AnyFunction], FunctionTool] | FunctionTool:
         """Decorator to register a tool.
 
@@ -721,6 +724,7 @@ class FastMCP(Generic[LifespanResultT]):
                 annotations=annotations,
                 exclude_args=exclude_args,
                 serializer=self._tool_serializer,
+                enabled=enabled,
             )
             self.add_tool(tool)
             return tool
@@ -749,6 +753,7 @@ class FastMCP(Generic[LifespanResultT]):
             tags=tags,
             annotations=annotations,
             exclude_args=exclude_args,
+            enabled=enabled,
         )
 
     def add_resource(self, resource: Resource, key: str | None = None) -> None:

src/fastmcp/tools/tool.py

@@ -62,6 +62,7 @@ class Tool(FastMCPComponent, ABC):
         annotations: ToolAnnotations | None = None,
         exclude_args: list[str] | None = None,
         serializer: Callable[[Any], str] | None = None,
+        enabled: bool | None = None,
     ) -> FunctionTool:
         """Create a Tool from a function."""
         return FunctionTool.from_function(
@@ -72,6 +73,7 @@ class Tool(FastMCPComponent, ABC):
             annotations=annotations,
             exclude_args=exclude_args,
             serializer=serializer,
+            enabled=enabled,
         )
 
     @abstractmethod
@@ -92,6 +94,7 @@ class Tool(FastMCPComponent, ABC):
         tags: set[str] | None = None,
         annotations: ToolAnnotations | None = None,
         serializer: Callable[[Any], str] | None = None,
+        enabled: bool | None = None,
     ) -> TransformedTool:
         from fastmcp.tools.tool_transform import TransformedTool
 
@@ -104,6 +107,7 @@ class Tool(FastMCPComponent, ABC):
             tags=tags,
             annotations=annotations,
             serializer=serializer,
+            enabled=enabled,
         )
 
 
@@ -120,6 +124,7 @@ class FunctionTool(Tool):
         annotations: ToolAnnotations | None = None,
         exclude_args: list[str] | None = None,
         serializer: Callable[[Any], str] | None = None,
+        enabled: bool | None = None,
     ) -> FunctionTool:
         """Create a Tool from a function."""
 
@@ -136,6 +141,7 @@ class FunctionTool(Tool):
             tags=tags or set(),
             annotations=annotations,
             serializer=serializer,
+            enabled=enabled if enabled is not None else True,
         )
 
     async def run(

src/fastmcp/tools/tool_transform.py

@@ -267,6 +267,7 @@ class TransformedTool(Tool):
         transform_args: dict[str, ArgTransform] | None = None,
         annotations: ToolAnnotations | None = None,
         serializer: Callable[[Any], str] | None = None,
+        enabled: bool | None = None,
     ) -> TransformedTool:
         """Create a transformed tool from a parent tool.
 
@@ -399,6 +400,7 @@ class TransformedTool(Tool):
             annotations=annotations or tool.annotations,
             serializer=serializer or tool.serializer,
             transform_args=transform_args,
+            enabled=enabled if enabled is not None else True,
         )
 
         return transformed_tool

tests/server/test_server_interactions.py

@@ -699,6 +699,93 @@ class TestToolContextInjection:
             assert result[0].text == "3"  # type: ignore[attr-defined]
 
 
+class TestToolEnabled:
+    async def test_toggle_enabled(self):
+        mcp = FastMCP()
+
+        @mcp.tool
+        def sample_tool(x: int) -> int:
+            return x * 2
+
+        assert sample_tool.enabled
+
+        tool = await mcp.get_tool("sample_tool")
+        assert tool.enabled
+
+        tool.disable()
+
+        assert not tool.enabled
+        assert not sample_tool.enabled
+
+        tool.enable()
+        assert tool.enabled
+        assert sample_tool.enabled
+
+    async def test_tool_disabled_in_decorator(self):
+        mcp = FastMCP()
+
+        @mcp.tool(enabled=False)
+        def sample_tool(x: int) -> int:
+            return x * 2
+
+        async with Client(mcp) as client:
+            tools = await client.list_tools()
+            assert len(tools) == 0
+
+    async def test_tool_toggle_enabled(self):
+        mcp = FastMCP()
+
+        @mcp.tool(enabled=False)
+        def sample_tool(x: int) -> int:
+            return x * 2
+
+        sample_tool.enable()
+
+        async with Client(mcp) as client:
+            tools = await client.list_tools()
+            assert len(tools) == 1
+
+    async def test_tool_toggle_disabled(self):
+        mcp = FastMCP()
+
+        @mcp.tool
+        def sample_tool(x: int) -> int:
+            return x * 2
+
+        sample_tool.disable()
+
+        async with Client(mcp) as client:
+            tools = await client.list_tools()
+            assert len(tools) == 0
+
+    async def test_get_tool_and_disable(self):
+        mcp = FastMCP()
+
+        @mcp.tool
+        def sample_tool(x: int) -> int:
+            return x * 2
+
+        tool = await mcp.get_tool("sample_tool")
+        assert tool.enabled
+
+        sample_tool.disable()
+
+        async with Client(mcp) as client:
+            result = await client.list_tools()
+            assert len(result) == 0
+
+    async def test_cant_call_disabled_tool(self):
+        mcp = FastMCP()
+
+        @mcp.tool(enabled=False)
+        def sample_tool(x: int) -> int:
+            return x * 2
+
+        with pytest.raises(Exception, match="Unknown tool"):
+            async with Client(mcp) as client:
+                await client.call_tool("sample_tool", {"x": 5})
+
+
 class TestResource:
     async def test_text_resource(self):
         mcp = FastMCP()