Add tool enable/disable functionality with client notifications

Author: davila7

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

@@ -8,7 +8,7 @@
 
 from mcp.server.fastmcp.exceptions import ToolError
 from mcp.server.fastmcp.utilities.func_metadata import FuncMetadata, func_metadata
-from mcp.types import ToolAnnotations
+from mcp.types import ServerNotification, ToolAnnotations, ToolListChangedNotification
 
 if TYPE_CHECKING:
     from mcp.server.fastmcp.server import Context
@@ -34,6 +34,7 @@ class Tool(BaseModel):
     annotations: ToolAnnotations | None = Field(
         None, description="Optional annotations for the tool"
     )
+    enabled: bool = Field(default=True, description="Whether the tool is enabled")
 
     @classmethod
     def from_function(
@@ -98,3 +99,29 @@ async def run(
             )
         except Exception as e:
             raise ToolError(f"Error executing tool {self.name}: {e}") from e
+
+    async def enable(
+        self, context: Context[ServerSessionT, LifespanContextT] | None = None
+    ) -> None:
+        """Enable the tool and notify clients."""
+        if not self.enabled:
+            self.enabled = True
+            if context and context.session:
+                notification = ToolListChangedNotification(
+                    method="notifications/tools/list_changed"
+                )
+                server_notification = ServerNotification.model_validate(notification)
+                await context.session.send_notification(server_notification)
+
+    async def disable(
+        self, context: Context[ServerSessionT, LifespanContextT] | None = None
+    ) -> None:
+        """Disable the tool and notify clients."""
+        if self.enabled:
+            self.enabled = False
+            if context and context.session:
+                notification = ToolListChangedNotification(
+                    method="notifications/tools/list_changed"
+                )
+                server_notification = ServerNotification.model_validate(notification)
+                await context.session.send_notification(server_notification)

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

@@ -28,8 +28,8 @@ def get_tool(self, name: str) -> Tool | None:
         return self._tools.get(name)
 
     def list_tools(self) -> list[Tool]:
-        """List all registered tools."""
-        return list(self._tools.values())
+        """List all enabled registered tools."""
+        return [tool for tool in self._tools.values() if tool.enabled]
 
     def add_tool(
         self,
@@ -61,4 +61,7 @@ async def call_tool(
         if not tool:
             raise ToolError(f"Unknown tool: {name}")
 
+        if not tool.enabled:
+            raise ToolError(f"Tool is disabled: {name}")
+
         return await tool.run(arguments, context=context)

tests/server/fastmcp/test_tool_manager.py

@@ -362,3 +362,52 @@ def echo(message: str) -> str:
         assert tools[0].annotations is not None
         assert tools[0].annotations.title == "Echo Tool"
         assert tools[0].annotations.readOnlyHint is True
+
+
+class TestToolEnableDisable:
+    """Test enabling and disabling tools."""
+
+    @pytest.mark.anyio
+    async def test_enable_disable_tool(self):
+        """Test enabling and disabling a tool."""
+
+        def add(a: int, b: int) -> int:
+            """Add two numbers."""
+            return a + b
+
+        manager = ToolManager()
+        tool = manager.add_tool(add)
+
+        # Tool should be enabled by default
+        assert tool.enabled is True
+
+        # Disable the tool
+        await tool.disable()
+        assert tool.enabled is False
+
+        # Enable the tool
+        await tool.enable()
+        assert tool.enabled is True
+
+    @pytest.mark.anyio
+    async def test_enable_disable_no_change(self):
+        """Test enabling and disabling a tool when there's no state change."""
+
+        def add(a: int, b: int) -> int:
+            """Add two numbers."""
+            return a + b
+
+        manager = ToolManager()
+        tool = manager.add_tool(add)
+
+        # Enable an already enabled tool (should not change state)
+        await tool.enable()
+        assert tool.enabled is True
+
+        # Disable the tool
+        await tool.disable()
+        assert tool.enabled is False
+
+        # Disable an already disabled tool (should not change state)
+        await tool.disable()
+        assert tool.enabled is False