Merge pull request #983 from jlowin/elicit-accept

Support implicit Elicitation acceptance

docs/clients/elicitation.mdx

@@ -35,7 +35,7 @@ Provide an `elicitation_handler` function when creating the client. FastMCP auto
 from fastmcp import Client
 from fastmcp.client.elicitation import ElicitResult
 
-async def elicitation_handler(message: str, response_type: type, params, context) -> ElicitResult:
+async def elicitation_handler(message: str, response_type: type, params, context):
     # Present the message to the user and collect input
     user_input = input(f"{message}: ")
     
@@ -43,7 +43,11 @@ async def elicitation_handler(message: str, response_type: type, params, context
     # FastMCP converted the JSON schema to this Python type for you
     response_data = response_type(value=user_input)
     
-    return ElicitResult(action="accept", content=response_data)
+    # You can return data directly - FastMCP will implicitly accept the elicitation
+    return response_data
+    
+    # Or explicitly return an ElicitResult for more control
+    # return ElicitResult(action="accept", content=response_data)
 
 client = Client(
     "my_mcp_server.py",
@@ -75,7 +79,7 @@ The elicitation handler receives four parameters:
 
 ### Response Actions
 
-The handler must return an `ElicitResult` object that includes both an action and (when accepted) the user's input:
+The handler can return data directly (which implicitly accepts the elicitation) or an `ElicitResult` object for more control over the response action:
 
 <Card icon="code" title="ElicitResult Structure">
 <ResponseField name="action" type="Literal['accept', 'decline', 'cancel']">
@@ -98,18 +102,20 @@ The handler must return an `ElicitResult` object that includes both an action an
 from fastmcp import Client
 from fastmcp.client.elicitation import ElicitResult
 
-async def basic_elicitation_handler(message: str, response_type: type, params, context) -> ElicitResult:
+async def basic_elicitation_handler(message: str, response_type: type, params, context):
     print(f"Server asks: {message}")
     
     # Simple text input for demonstration
     user_response = input("Your response: ")
     
     if not user_response:
+        # For non-acceptance, use ElicitResult explicitly
         return ElicitResult(action="decline")
     
     # Use the response_type dataclass to create a properly structured response
     # FastMCP handles the conversion from JSON schema to Python type
-    return ElicitResult(action="accept", content=response_type(value=user_response))
+    # Return data directly - FastMCP will implicitly accept the elicitation
+    return response_type(value=user_response)
 
 client = Client(
     "my_mcp_server.py", 

src/fastmcp/client/elicitation.py

@@ -29,7 +29,7 @@ ElicitationHandler: TypeAlias = Callable[
         ElicitRequestParams,
         RequestContext[ClientSession, LifespanContextT],
     ],
-    Awaitable[ElicitResult[T | dict[str, Any]]],
+    Awaitable[T | dict[str, Any] | ElicitResult[T | dict[str, Any]]],
 ]
 
 
@@ -46,6 +46,9 @@ def create_elicitation_callback(
             result = await elicitation_handler(
                 params.message, response_type, params, context
             )
+            # if the user returns data, we assume they've accepted the elicitation
+            if not isinstance(result, ElicitResult):
+                result = ElicitResult(action="accept", content=result)
             content = to_jsonable_python(result.content)
             return MCPElicitResult(**result.model_dump() | {"content": content})
         except Exception as e:

tests/client/test_streamable_http.py

@@ -28,6 +28,15 @@ def fastmcp_server():
         """Greet someone by name."""
         return f"Hello, {name}!"
 
+    @server.tool
+    async def elicit(ctx: Context) -> str:
+        """Elicit a response from the user."""
+        result = await ctx.elicit("What is your name?", response_type=str)
+        if result.action == "accept":
+            return f"You said your name was: {result.data}!"
+        else:
+            return "No name provided"
+
     # Add a second tool
     @server.tool
     def add(a: int, b: int) -> int:
@@ -170,6 +179,21 @@ async def test_greet_with_progress_tool(streamable_http_server: str):
         progress_handler.assert_called_once_with(0.5, 1.0, "Greeting in progress")
 
 
+@pytest.mark.parametrize("streamable_http_server", [True, False], indirect=True)
+async def test_elicitation_tool(streamable_http_server: str):
+    """Test calling the elicitation tool in both stateless and stateful modes."""
+
+    async def elicitation_handler(message, response_type, params, ctx):
+        return {"value": "Alice"}
+
+    async with Client(
+        transport=StreamableHttpTransport(streamable_http_server),
+        elicitation_handler=elicitation_handler,
+    ) as client:
+        result = await client.call_tool("elicit")
+        assert result.data == "You said your name was: Alice!"
+
+
 async def test_nested_streamable_http_server_resolves_correctly():
     # tests patch for
     # https://github.com/modelcontextprotocol/python-sdk/pull/659