Handler must be async; add to sessionkwargs

src/fastmcp/client/client.py

@@ -252,7 +252,9 @@ class Client(Generic[ClientTransportT]):
             sampling_callback
         )
 
-    def set_elicitation_callback(self, elicitation_callback: ElicitationHandler) -> None:
+    def set_elicitation_callback(
+        self, elicitation_callback: ElicitationHandler
+    ) -> None:
         """Set the elicitation callback for the client."""
         self._session_kwargs["elicitation_callback"] = create_elicitation_callback(
             elicitation_callback

src/fastmcp/client/elicitation.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import inspect
 from collections.abc import Awaitable, Callable
 from typing import Any, TypeAlias
 
@@ -19,7 +18,7 @@ ElicitationHandler: TypeAlias = Callable[
         dict[str, Any],  # requested_schema
         RequestContext[ClientSession, LifespanContextT],
     ],
-    ElicitResult | Awaitable[ElicitResult],
+    Awaitable[ElicitResult],
 ]
 
 
@@ -31,12 +30,9 @@ def create_elicitation_callback(
         params: ElicitRequestParams,
     ) -> ElicitResult | mcp.types.ErrorData:
         try:
-            result = elicitation_handler(
+            result = await elicitation_handler(
                 params.message, params.requestedSchema, context
             )
-            if inspect.isawaitable(result):
-                result = await result
-
             return result
         except Exception as e:
             return mcp.types.ErrorData(

src/fastmcp/client/transports.py

@@ -15,7 +15,13 @@ import anyio
 import httpx
 import mcp.types
 from mcp import ClientSession, StdioServerParameters
-from mcp.client.session import ListRootsFnT, LoggingFnT, MessageHandlerFnT, SamplingFnT
+from mcp.client.session import (
+    ElicitationFnT,
+    ListRootsFnT,
+    LoggingFnT,
+    MessageHandlerFnT,
+    SamplingFnT,
+)
 from mcp.server.fastmcp import FastMCP as FastMCP1Server
 from mcp.shared.memory import create_client_server_memory_streams
 from pydantic import AnyUrl
@@ -56,6 +62,7 @@ class SessionKwargs(TypedDict, total=False):
     sampling_callback: SamplingFnT | None
     list_roots_callback: ListRootsFnT | None
     logging_callback: LoggingFnT | None
+    elicitation_callback: ElicitationFnT | None
     message_handler: MessageHandlerFnT | None
     client_info: mcp.types.Implementation | None
 

tests/client/test_elicitation.py

@@ -5,6 +5,7 @@ from mcp.types import ElicitResult
 
 from fastmcp import Context, FastMCP
 from fastmcp.client.client import Client
+from fastmcp.exceptions import ToolError
 from fastmcp.server.elicitation import (
     AcceptedElicitation,
     CancelledElicitation,
@@ -38,6 +39,14 @@ def fastmcp_server():
     return mcp
 
 
+async def test_elicitation_with_no_handler(fastmcp_server):
+    """Test that elicitation works without a handler."""
+
+    async with Client(fastmcp_server) as client:
+        with pytest.raises(ToolError, match="Elicitation not supported"):
+            await client.call_tool("ask_for_name", {})
+
+
 async def test_elicitation_accept_content(fastmcp_server):
     """Test basic elicitation functionality."""
 
@@ -49,7 +58,7 @@ async def test_elicitation_accept_content(fastmcp_server):
         fastmcp_server, elicitation_handler=elicitation_handler
     ) as client:
         result = await client.call_tool("ask_for_name", {})
-        assert result[0].text == "Hello, Alice!"  # type: ignore[attr-defined]
+        assert result.data == "Hello, Alice!"
 
 
 async def test_elicitation_decline(fastmcp_server):
@@ -62,7 +71,7 @@ async def test_elicitation_decline(fastmcp_server):
         fastmcp_server, elicitation_handler=elicitation_handler
     ) as client:
         result = await client.call_tool("ask_for_name", {})
-        assert result[0].text == "No name provided."  # type: ignore[attr-defined]
+        assert result.data == "No name provided."
 
 
 async def test_default_response_type(fastmcp_server):
@@ -86,7 +95,7 @@ async def test_default_response_type(fastmcp_server):
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("ask_for_color", {})
-        assert result[0].text == "Your favorite color is blue!"  # type: ignore[attr-defined]
+        assert result.data == "Your favorite color is blue!"
 
 
 async def test_elicitation_handler_parameters():
@@ -148,7 +157,7 @@ async def test_elicitation_default_string_schema():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("ask_for_input", {})
-        assert result[0].text == "You said: Hello world!"  # type: ignore[attr-defined]
+        assert result.data == "You said: Hello world!"
 
 
 async def test_elicitation_cancel_action():
@@ -172,7 +181,7 @@ async def test_elicitation_cancel_action():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("ask_for_optional_info", {})
-        assert result[0].text == "Request was canceled"  # type: ignore[attr-defined]
+        assert result.data == "Request was canceled"
 
 
 async def test_elicitation_number_schema():
@@ -198,7 +207,7 @@ async def test_elicitation_number_schema():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("get_age", {})
-        assert result[0].text == "You are 25 years old"  # type: ignore[attr-defined]
+        assert result.data == "You are 25 years old"
 
 
 async def test_elicitation_handler_error():
@@ -219,7 +228,7 @@ async def test_elicitation_handler_error():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("failing_elicit", {})
-        assert "Error:" in result[0].text  # type: ignore[attr-defined]
+        assert "Error:" in result.data
 
 
 async def test_elicitation_multiple_calls():
@@ -272,7 +281,7 @@ async def test_elicitation_multiple_calls():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("multi_step_form", {})
-        assert result[0].text == "Hello Bob, you are 25 years old"  # type: ignore[attr-defined]
+        assert result.data == "Hello Bob, you are 25 years old"
         assert call_count == 2
 
 
@@ -307,7 +316,7 @@ async def test_dataclass_response_type():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("get_user_info", {})
-        assert result[0].text == "User: Alice, age: 30"  # type: ignore[attr-defined]
+        assert result.data == "User: Alice, age: 30"
 
 
 async def test_primitive_type_string():
@@ -326,7 +335,7 @@ async def test_primitive_type_string():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("test_string", {})
-        assert result[0].text == "Got: hello"  # type: ignore[attr-defined]
+        assert result.data == "Got: hello"
 
 
 async def test_primitive_type_int():
@@ -345,7 +354,7 @@ async def test_primitive_type_int():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("test_int", {})
-        assert result[0].text == "Got: 42"  # type: ignore[attr-defined]
+        assert result.data == "Got: 42"
 
 
 async def test_primitive_type_float():
@@ -364,7 +373,7 @@ async def test_primitive_type_float():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("test_float", {})
-        assert result[0].text == "Got: 3.14"  # type: ignore[attr-defined]
+        assert result.data == "Got: 3.14"
 
 
 async def test_primitive_type_bool():
@@ -383,7 +392,7 @@ async def test_primitive_type_bool():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("test_bool", {})
-        assert result[0].text == "Got: True"  # type: ignore[attr-defined]
+        assert result.data == "Got: True"
 
 
 async def test_schema_validation_rejects_non_object():
@@ -458,7 +467,7 @@ async def test_pattern_matching_accept():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("pattern_match_tool", {})
-        assert result[0].text == "Hello Alice!"  # type: ignore[attr-defined]
+        assert result.data == "Hello Alice!"
 
 
 async def test_pattern_matching_decline():
@@ -482,7 +491,7 @@ async def test_pattern_matching_decline():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("pattern_match_tool", {})
-        assert result[0].text == "You declined"  # type: ignore[attr-defined]
+        assert result.data == "You declined"
 
 
 async def test_pattern_matching_cancel():
@@ -506,4 +515,4 @@ async def test_pattern_matching_cancel():
 
     async with Client(mcp, elicitation_handler=elicitation_handler) as client:
         result = await client.call_tool("pattern_match_tool", {})
-        assert result[0].text == "Cancelled"  # type: ignore[attr-defined]
+        assert result.data == "Cancelled"