Missing required parameter: 'messages[1].tool_calls[1].function.arguments'

[dmingolla]

Hello,
when I run some prompts I get the following error:

Missing required parameter: 'messages[1].tool_calls[1].function.arguments'

This error is not always happening, I think it depends on how the model pass the value of the arguments of the tool that can be empty

I tried to:

• test the same prompt on gpt4o-mini and gpt4o but it doesn't work
• test the same prompt and model on Warp and it works perfectly, so there is no issue in my mcp server code and the issue is not due to the model's intelligence

My mcphost config file:

{
  "mcpServers": {
    "mcp-server": {
      "type": "local",
      "command": [
        "uv",
        "run",
        "-p",
        "/home/demo/mcp/.venv/bin/python",
        "--",
        "/home/demo/mcp/main.py",
        "--allow-write"
      ],
      "cwd": "/home/demo/mcp"
    }
  },
  "model": "${env://MODEL:-openai:gpt-4o-mini}",
  "provider-api-key": "${env://OPENAI_API_KEY}",
  "max-tokens": 16000
}