Inspector does not report log messages

[ezyang]

Describe the bug
Inspector does not report log messages. It does report progress. We know the log messages are being emitted because Claude Desktop reports them.

To Reproduce

# progress_demo.py
import asyncio
from mcp.server.fastmcp import FastMCP, Context

# Create an MCP server
mcp = FastMCP("Progress Demo")

@mcp.tool()
async def slow_process(duration: float = 5.0, steps: int = 50, ctx: Context = None) -> str:
    """Simulate a slow process while reporting progress.
    
    Args:
        duration: Total duration in seconds (default: 5.0)
        steps: Number of progress steps to report (default: 50)
        ctx: MCP context (automatically injected)
    
    Returns:
        A completion message
    """
    if ctx is None:
        return "Error: Context not available"
    
    sleep_interval = duration / steps
    
    ctx.info(f"Starting slow process: {duration} seconds with {steps} updates")
    
    for i in range(steps + 1):
        # Calculate and report progress percentage
        progress_pct = i / steps
        await ctx.report_progress(i, steps)
        
        # Add some detailed info about the current step
        if i % 5 == 0:
            await ctx.info(f"Processing step {i}/{steps} ({progress_pct:.0%} complete)")
        
        # Sleep for the calculated interval
        await asyncio.sleep(sleep_interval)
    
    ctx.info("Process completed successfully!")
    return f"Successfully completed slow process in {duration} seconds"


if __name__ == "__main__":
    # Run the server directly when the script is executed
    mcp.run()

Run it with inspector, trigger the tool, see only report progress in the window.
Run it with Claude Desktop, look at the mcp log

2025-03-12T04:04:14.665Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 0/50 (0% complete)"}}
2025-03-12T04:04:15.171Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 5/50 (10% complete)"}}
2025-03-12T04:04:15.676Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 10/50 (20% complete)"}}
2025-03-12T04:04:16.182Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 15/50 (30% complete)"}}
2025-03-12T04:04:16.688Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 20/50 (40% complete)"}}
2025-03-12T04:04:17.193Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 25/50 (50% complete)"}}
2025-03-12T04:04:17.698Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 30/50 (60% complete)"}}
2025-03-12T04:04:18.203Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 35/50 (70% complete)"}}
2025-03-12T04:04:18.709Z [Progress Demo] [info] Message from server: {"jsonrpc":"2.0","method":"notifications/message","params":{"level":"info","data":"Processing step 40/50 (80% complete)"}}
2025-03-12T04:04:18.937Z [Progress Demo] [info] Message from client: {"method":"resources/list","params":{},"jsonrpc":"2.0","id":12}

Amusingly, Claude Desktop doesn't report the progress in the logs at all, but that's not really this bug.

Expected behavior
Inspector should show us the logs.

Screenshots

Desktop (please complete the following information):

• OS: OSX
• Chrome
• 133

[Nriver]

I find that using loguru for logging works well in the inspector.

from loguru import logger

logger.info("bla bla")

[ezyang]

Oh, to be clear, I don't have any problem logging my code some other way. But I was hoping one day Claude Desktop would surface log messages to the user as the tool was executing (which would necessitate messages over MCP)

[cliffhall]

I've got this one fixed locally, and will submit a PR shortly.

I was in the Inspector just the other day, adding resource subscriptions, and I needed to add a handler for the notification type in useConnection.ts. That's all I needed to do to enable server logging messages.

In order to generate the logging, I wanted to do it all from the MCP project reference servers, not FastMCP, just to rule out any problems that could have been associated with that. And also I'm more of a typescript guy.

I expected the everything server to do this, as it also sent dummy resource subscription update messages. It didn't so I added that and will make a PR to that project as well. It just generates a random-leveled logging message every 15 seconds.