How to receive notifications on mcp client side?

[shashisingh]

I am trying to send few logging events to the client during a tool invocation. I am using "Context.info('Hello)" inside a mcp.tool decorated function. I am using FASTMcp for hosting tools. I was expecting to receive these notifications in my ClientSession's "_received_notification" method. But I don't seem to get this to work. I do not see that _received_notification is getting called.

[kylestratis]

👍
It doesn't seem like notification handling is yet built into the Python SDK

[maxisbey]

The SDK partially supports receiving notifications on the client side today:

Notification Type	Current Support
LoggingMessageNotification	✅ logging_callback
ProgressNotification	✅ progress_callback on call_tool()
CancelledNotification	✅ Automatic
ResourceListChangedNotification	❌ message_handler only
ResourceUpdatedNotification	❌ message_handler only
ToolListChangedNotification	❌ message_handler only
PromptListChangedNotification	❌ message_handler only
ElicitCompleteNotification	❌ message_handler only
TaskStatusNotification	❌ message_handler only

For logging notifications (Context.info(), etc.), pass a logging_callback to ClientSession:

async def handle_log(params: types.LoggingMessageNotificationParams) -> None:
    print(f"[{params.level}] {params.data}")

async with ClientSession(read, write, logging_callback=handle_log) as session:
    ...

For progress notifications, pass a progress_callback when calling a tool:

await session.call_tool("my_tool", {}, progress_callback=on_progress)

For other notifications (resource/tool/prompt list changes, etc.), use the generic message_handler parameter:

from mcp.shared.session import RequestResponder
import mcp.types as types

async def handle_notifications(
    message: RequestResponder[types.ServerRequest, types.ClientResult] | types.ServerNotification | Exception,
) -> None:
    if isinstance(message, types.ServerNotification):
        match message.root:
            case types.ResourceListChangedNotification():
                print("Resources changed, refreshing list...")
            case types.ToolListChangedNotification():
                print("Tools changed, refreshing list...")
            case types.PromptListChangedNotification():
                print("Prompts changed, refreshing list...")

async with ClientSession(read, write, message_handler=handle_notifications) as session:
    ...

We do want to add proper dedicated callbacks for all notification types. PR #1611 addresses this but hasn't been reviewed yet.

As this issue is quite old, I'm closing it for now. Feel free to re-open if you have further questions.

_{AI Disclaimer}