Connection close Issue on Claude Desktop

[nicodeg87]

Hi guys,

I tried to configure the proxy to use a MCP remote Server which is provided with stdio transport on Claude desktop. I managed to get it working, the tools are properly displayed on Claude and the first tool execution works well, but after the first execution it looks that for some reason Claude is disconnected from the MCP server.

• The logs I see on the proxy for the stdio mcp server is:
  DEBUG:sse_starlette.sse:Got event: http.disconnect. Stop streaming.

• The logs I see on the on Claude logs (~/Library/Logs/Claude/mcp.log)
  2025-03-24T00:26:10.587Z [info] [test-proxy] Server transport closed
2025-03-24T00:26:10.587Z [info] [test-proxy] Client transport closed
2025-03-24T00:26:10.588Z [info] [test-proxy] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. console.error('...')in JavaScript,print('...', file=sys.stderr) in python) and it will appear in this log.
2025-03-24T00:26:10.588Z [error] [test-proxy] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging)
2025-03-24T00:26:10.589Z [info] [test-proxy] Client transport closed

• This is the claude config im using (note that im running the "stdio to sse" proxy on docker):
  { "mcpServers": { "test-proxy": { "command": "docker", "args": [ "run", "--rm", "-i", "ghcr.io/sparfenyuk/mcp-proxy:latest", "http://host.docker.internal:8080/sse" ], "env": {} } } }

Note: Im doing this PoC because im planning to run the sse mcp server remotely, for now im testing it locally.

Any idea what can be causing the issue?
Thanks in advance.

[nicodeg87]

Another interesting behavior on the Claude logs is that while the tool is executed I see timeout errors (looks like the sse mcp server is not hable to handle other requests while the tool is running)

2025-03-24T00:26:00.180Z [info] [test-proxy] Message from client: {"jsonrpc":"2.0","method":"notifications/cancelled","params":{"requestId":29,"reason":"Error: MCP error -32001: Request timed out"}}
2025-03-24T00:26:05.176Z [info] [test-proxy] Message from client: {"method":"resources/list","params":{},"jsonrpc":"2.0","id":32}
2025-03-24T00:26:05.177Z [info] [test-proxy] Message from client: {"jsonrpc":"2.0","method":"notifications/cancelled","params":{"requestId":30,"reason":"Error: MCP error -32001: Request timed out"}}
2025-03-24T00:26:05.177Z [info] [test-proxy] Message from client: {"method":"prompts/list","params":{},"jsonrpc":"2.0","id":33}
2025-03-24T00:26:05.179Z [info] [test-proxy] Message from client: {"jsonrpc":"2.0","method":"notifications/cancelled","params":{"requestId":31,"reason":"Error: MCP error -32001: Request timed out"}}
2025-03-24T00:26:10.176Z [info] [test-proxy] Message from client: {"method":"resources/list","params":{},"jsonrpc":"2.0","id":34}
2025-03-24T00:26:10.177Z [info] [test-proxy] Message from client: {"jsonrpc":"2.0","method":"notifications/cancelled","params":{"requestId":32,"reason":"Error: MCP error -32001: Request timed out"}}
2025-03-24T00:26:10.177Z [info] [test-proxy] Message from client: {"method":"prompts/list","params":{},"jsonrpc":"2.0","id":35}

[sparfenyuk]

Hey @nicodeg87 , thanks for reporting this.

I can't reproduce the first issue you described.

Regarding the second one — yes, I can confirm. Will try to understand the root cause. At least, more than one client connected to the proxy correlates with timeouts.

[sparfenyuk]

Regarding the first issue, can you replicate the behavior using the inspector? Run command npx @modelcontextprotocol/inspector@0.3.0 and configure and establish the connections, and then send commands as Claude does. If anything happens, you'll see more logs.