Support enabled/disabled prompts

src/fastmcp/prompts/prompt.py

@@ -96,6 +96,7 @@ class Prompt(FastMCPComponent, ABC):
         name: str | None = None,
         description: str | None = None,
         tags: set[str] | None = None,
+        enabled: bool | None = None,
     ) -> FunctionPrompt:
         """Create a Prompt from a function.
 
@@ -106,7 +107,7 @@ class Prompt(FastMCPComponent, ABC):
         - A sequence of any of the above
         """
         return FunctionPrompt.from_function(
-            fn=fn, name=name, description=description, tags=tags
+            fn=fn, name=name, description=description, tags=tags, enabled=enabled
         )
 
     @abstractmethod
@@ -130,6 +131,7 @@ class FunctionPrompt(Prompt):
         name: str | None = None,
         description: str | None = None,
         tags: set[str] | None = None,
+        enabled: bool | None = None,
     ) -> FunctionPrompt:
         """Create a Prompt from a function.
 
@@ -195,6 +197,7 @@ class FunctionPrompt(Prompt):
             description=description,
             arguments=arguments,
             tags=tags or set(),
+            enabled=enabled if enabled is not None else True,
             fn=fn,
         )
 

src/fastmcp/prompts/prompt_manager.py

@@ -40,9 +40,11 @@ class PromptManager:
 
         self.duplicate_behavior = duplicate_behavior
 
-    def get_prompt(self, key: str) -> Prompt | None:
+    def get_prompt(self, key: str) -> Prompt:
         """Get prompt by key."""
-        return self._prompts.get(key)
+        if key in self._prompts:
+            return self._prompts[key]
+        raise NotFoundError(f"Unknown prompt: {key}")
 
     def get_prompts(self) -> dict[str, Prompt]:
         """Get all registered prompts, indexed by registered key."""

src/fastmcp/server/server.py

@@ -940,6 +940,7 @@ class FastMCP(Generic[LifespanResultT]):
         name: str | None = None,
         description: str | None = None,
         tags: set[str] | None = None,
+        enabled: bool | None = None,
     ) -> FunctionPrompt: ...
 
     @overload
@@ -950,6 +951,7 @@ class FastMCP(Generic[LifespanResultT]):
         name: str | None = None,
         description: str | None = None,
         tags: set[str] | None = None,
+        enabled: bool | None = None,
     ) -> Callable[[AnyFunction], FunctionPrompt]: ...
 
     def prompt(
@@ -959,6 +961,7 @@ class FastMCP(Generic[LifespanResultT]):
         name: str | None = None,
         description: str | None = None,
         tags: set[str] | None = None,
+        enabled: bool | None = None,
     ) -> Callable[[AnyFunction], FunctionPrompt] | FunctionPrompt:
         """Decorator to register a prompt.
 
@@ -1050,6 +1053,7 @@ class FastMCP(Generic[LifespanResultT]):
                 name=prompt_name,
                 description=description,
                 tags=tags,
+                enabled=enabled,
             )
             self.add_prompt(prompt)
 
@@ -1077,6 +1081,7 @@ class FastMCP(Generic[LifespanResultT]):
             name=prompt_name,
             description=description,
             tags=tags,
+            enabled=enabled,
         )
 
     async def run_stdio_async(self) -> None:

tests/server/test_proxy.py

@@ -178,7 +178,9 @@ class TestResources:
         assert json.loads(result[0].text) == USERS  # type: ignore[attr-defined]
 
     async def test_read_resource_returns_none_if_not_found(self, proxy_server):
-        with pytest.raises(McpError, match="Unknown resource: resource://nonexistent"):
+        with pytest.raises(
+            McpError, match="Unknown resource: 'resource://nonexistent'"
+        ):
             async with Client(proxy_server) as client:
                 await client.read_resource("resource://nonexistent")
 

tests/server/test_server_interactions.py

@@ -1220,6 +1220,93 @@ class TestPrompts:
         assert prompt.tags == {"example", "test-tag"}
 
 
+class TestPromptEnabled:
+    async def test_toggle_enabled(self):
+        mcp = FastMCP()
+
+        @mcp.prompt
+        def sample_prompt() -> str:
+            return "Hello, world!"
+
+        assert sample_prompt.enabled
+
+        prompt = await mcp.get_prompt("sample_prompt")
+        assert prompt.enabled
+
+        prompt.disable()
+
+        assert not prompt.enabled
+        assert not sample_prompt.enabled
+
+        prompt.enable()
+        assert prompt.enabled
+        assert sample_prompt.enabled
+
+    async def test_prompt_disabled_in_decorator(self):
+        mcp = FastMCP()
+
+        @mcp.prompt(enabled=False)
+        def sample_prompt() -> str:
+            return "Hello, world!"
+
+        async with Client(mcp) as client:
+            prompts = await client.list_prompts()
+            assert len(prompts) == 0
+
+    async def test_prompt_toggle_enabled(self):
+        mcp = FastMCP()
+
+        @mcp.prompt(enabled=False)
+        def sample_prompt() -> str:
+            return "Hello, world!"
+
+        sample_prompt.enable()
+
+        async with Client(mcp) as client:
+            prompts = await client.list_prompts()
+            assert len(prompts) == 1
+
+    async def test_prompt_toggle_disabled(self):
+        mcp = FastMCP()
+
+        @mcp.prompt
+        def sample_prompt() -> str:
+            return "Hello, world!"
+
+        sample_prompt.disable()
+
+        async with Client(mcp) as client:
+            prompts = await client.list_prompts()
+            assert len(prompts) == 0
+
+    async def test_get_prompt_and_disable(self):
+        mcp = FastMCP()
+
+        @mcp.prompt
+        def sample_prompt() -> str:
+            return "Hello, world!"
+
+        prompt = await mcp.get_prompt("sample_prompt")
+        assert prompt.enabled
+
+        sample_prompt.disable()
+
+        async with Client(mcp) as client:
+            result = await client.list_prompts()
+            assert len(result) == 0
+
+    async def test_cant_get_disabled_prompt(self):
+        mcp = FastMCP()
+
+        @mcp.prompt(enabled=False)
+        def sample_prompt() -> str:
+            return "Hello, world!"
+
+        with pytest.raises(McpError, match="Unknown prompt"):
+            async with Client(mcp) as client:
+                await client.get_prompt("sample_prompt")
+
+
 class TestPromptContext:
     async def test_prompt_context(self):
         mcp = FastMCP()