Logging

mcp-use supports this feature through a logging_callback function that can be passed to the MCPClient.

Server-Side: Sending Logs

On the server (using fastmcp), you can send log messages with different severity levels from within a tool’s context (ctx).

from fastmcp import Context, FastMCP

mcp = FastMCP(name="PrimitiveServer")

@mcp.tool()
async def logging_tool(ctx: Context) -> str:
    """Log a message to the client."""
    await ctx.debug("This is a debug message")
    await ctx.info("This is an info message")
    await ctx.warning("This is a warning message")
    await ctx.error("This is an error message")
    return "Logging tool completed"

These log messages are sent as logging/message notifications to the client.

Client-Side: Handling Logs

While you can catch LoggingMessageNotification events within the general message_handler, the recommended approach is to use the dedicated logging_callback. This keeps your code clean by separating logging concerns from other notification handling. The logging_callback receives the parameters of the log notification directly, which include the level and message.

import asyncio
import mcp.types as types
from mcp_use import MCPClient

# A dedicated handler for log messages
async def handle_logs(log_params: types.LoggingMessageNotificationParams):
    print(f"LOG [{log_params.level.upper()}]: {log_params.message}")

async def test_logging(primitive_server):
    """Tests receiving logs from the primitive server."""
    config = {"mcpServers": {"PrimitiveServer": {"url": f"{primitive_server}/mcp"}}}
    # Pass the callback to the client
    client = MCPClient(config, logging_callback=handle_logs)
    try:
        await client.create_all_sessions()
        session = client.get_session("PrimitiveServer")

        # This tool will trigger the logging_callback
        result = await session.call_tool(name="logging_tool", arguments={})
        assert result.content[0].text == "Logging tool completed"
    finally:
        await client.close_all_sessions()

By using the logging_callback, you can easily route server-side logs to your client’s logging system, display them in a debug console, or handle them in any other way that suits your application’s needs.

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Server-Side: Sending Logs

Client-Side: Handling Logs

​Server-Side: Sending Logs

​Client-Side: Handling Logs

Server-Side: Sending Logs

Client-Side: Handling Logs