Claude config file issue: tool works, but creats loads of error messages

[dakoller]

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Your Question

My Claude config file looks like this:

{ "mcpServers": { "mcp-obsidian": { "command": "npx", "args": [ "-y", "@smithery/cli@latest", "run", "mcp-obsidian", "--config", "\"{\\\"vaultPath\\\":\\\"/Users/dakoller/Library/Mobile Documents/iCloud~md~obsidian/Documents/dkVault\\\"}\"" ] }, "mcp-palino-booklist": { "command": "/Users/dakoller/anaconda3/bin/uv", "args": [ "--directory", "/Users/dakoller/projects/mcp-palino-booklist", "run", "booklist.py" ] } } }

While the tools works as intended, it creates loads of error messages, where I cannot find the source of the issue:

It is difficult to see where position 5 is and adding a comma after the args array does not solve the problem.

Added Information:

I am using the python-sdk to provide the function and have now worked with MCP-Inspector as well. The issue also comes up on the commandline when using the Inspector, which tells me that the issue is not in the config file.

The request from the MCP Inspector is:
{ "method": "tools/call", "params": { "name": "get_book_list", "arguments": {}, "_meta": { "progressToken": 3 } } }

The obviously faulty response is:
{ "content": [ { "type": "text", "text": "978-3-949375-04-0, 978-3-949375-07-1, 978-3-949375-08-8, 978-3-949375-09-5, 978-3-949375-10-1, 978-3-949375-11-8" } ], "isError": false }

I originally returned the python list from this method, because I thought that maybe some serialization issue prohibits me from returning a python list. Now I am using a simple text, but the error message is still the same.

The JSON validation does not return any error in the JSON.

[olaservo]

It seems like your mcp-palino-booklist server could be having trouble parsing a different JSON file since the Claude config syntax looks correct. Is your booklist server code using JSON?

[Mehdi-Bl]

This might be a Json encoding issue in your tool response.
Ensure you correctly encore booklist.py response for Json output

[dakoller]

Closing the issue here, since I created an issue the python-sdk repository. modelcontextprotocol/python-sdk#290