fastmcp/docs/clients/logging.mdx

---
title: Server Logging
sidebarTitle: Logging
description: Receive and handle log messages from MCP servers.
icon: receipt
---

import { VersionBadge } from '/snippets/version-badge.mdx'

<VersionBadge version="2.0.0" />

MCP servers can emit log messages to clients. The client can handle these logs through a log handler callback.

## Setting Up Log Handling

Provide a `log_handler` function when creating the client:

```python
from fastmcp import Client
from fastmcp.client.logging import LogMessage

async def log_handler(message: LogMessage):
    level = message.level.upper()
    logger = message.logger or 'server'
    data = message.data
    print(f"[{level}] {logger}: {data}")

client = Client(
    "my_mcp_server.py",
    log_handler=log_handler,
)
```

## LogMessage Structure

The `log_handler` receives a `LogMessage` object with:

- **`level`**: Log level (e.g., "debug", "info", "warning", "error")
- **`logger`**: Logger name (optional, may be None)
- **`data`**: The actual log message content

```python
async def detailed_log_handler(message: LogMessage):
    if message.level == "error":
        print(f"ERROR: {message.data}")
    elif message.level == "warning":
        print(f"WARNING: {message.data}")
    else:
        print(f"{message.level.upper()}: {message.data}")
```

## Default Log Handling

If you don't provide a custom `log_handler`, FastMCP uses a default handler that emits DEBUG level logs:

```python
# Without custom handler - uses default DEBUG logging
client = Client("my_mcp_server.py")

async with client:
    # Server logs will be emitted at DEBUG level
    await client.call_tool("some_tool")
```