modelcontextprotocol · davila7 · May 15, 2025 · May 15, 2025 · May 16, 2025 · May 16, 2025
diff --git a/README.md b/README.md
@@ -30,10 +30,12 @@
    - [Prompts](#prompts)
    - [Images](#images)
    - [Context](#context)
+    - [Authentication](#authentication)
  - [Running Your Server](#running-your-server)
    - [Development Mode](#development-mode)
    - [Claude Desktop Integration](#claude-desktop-integration)
    - [Direct Execution](#direct-execution)
+    - [Streamable HTTP Transport](#streamable-http-transport)
    - [Mounting to an Existing ASGI Server](#mounting-to-an-existing-asgi-server)
  - [Examples](#examples)
    - [Echo Server](#echo-server)
@@ -243,6 +245,19 @@ async def fetch_weather(city: str) -> str:
    async with httpx.AsyncClient() as client:
        response = await client.get(f"https://api.weather.com/{city}")
        return response.text
+
+
+tool = mcp._tool_manager.get_tool("fetch_weather")
+
+
+async def disable_tool():
+    # Disable the tool temporarily
+    await tool.disable(mcp.get_context())
+
+
+async def enable_tool():
+    # Re-enable the tool when needed
+    await tool.enable(mcp.get_context())
 ```

 ### Prompts

diff --git a/src/mcp/server/fastmcp/tools/base.py b/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)
diff --git a/src/mcp/server/fastmcp/tools/tool_manager.py b/src/mcp/server/fastmcp/tools/tool_manager.py
@@ -39,8 +39,8 @@ 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,
@@ -72,4 +72,7 @@ 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)
diff --git a/tests/server/fastmcp/test_tool_manager.py b/tests/server/fastmcp/test_tool_manager.py
@@ -392,3 +392,52 @@ 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
-Original file line number
+Diff line change
@@ -39,8 +39,8 @@ 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,
@@ -72,4 +72,7 @@ async def call_tool(
             if not tool:
                 raise ToolError(f"Unknown tool: {name}")
+            if not tool.enabled:
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            bzsurbhi
  

      

      

      


        May 20, 2025


      
    

  


        
      
  
  
  
    

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      Should we add similar checks in call_tool() and get_tool() as well?
    
  
  


    

        
      
  
    
  
  
  
    
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            davila7
  

      

      

      


        May 20, 2025


      
    

  


        
      
  
  
  
    

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      For call_tool() we already have the necessary validation checking if the tool is enabled.
And for get_tool(), I think we don't need to add this validation. We retrieve in get_tool() and validate in call_tool() where the tool is actually used.

This keeps the code cleaner and lets us access disabled tools when needed (for inspection, etc).
    
  
  


    

        
      
  
    
  
  
  
    
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+                raise ToolError(f"Tool is disabled: {name}")
             return await tool.run(arguments, context=context)