list_backtests fails: parameterSet is [] but MCP model expects dict

[npschweizer]

Summary

list_backtests fails with Pydantic validation errors on BacktestSummaryResponse.parameterSet.
The API returns parameterSet: [] but the MCP model expects a dict, so deserialization fails for every backtest.

---

Environment

• MCP image: mcp/quantconnect:latest
• Host OS: macOS (Apple Silicon / Intel) – macOS VERSION_HERE
• Docker: 29.2.0
• Client: OpenCode / MCP host using this config:

"mcp": {
  "quantconnect": {
    "type": "local",
    "command": [
      "docker",
      "run",
      "-i",
      "--rm",
      "-e", "QUANTCONNECT\_USER\_ID",
      "-e", "QUANTCONNECT\_API\_TOKEN",
      "-e", "QUANTCONNECT\_ORGANIZATION\_ID",
      "mcp/quantconnect"
    ],
    "enabled": true,
    "environment": {
      "QUANTCONNECT\_USER\_ID": "{env:QUANTCONNECT\_USER\_ID}",
      "QUANTCONNECT\_API\_TOKEN": "{env:QUANTCONNECT\_API\_TOKEN}",
      "QUANTCONNECT\_ORGANIZATION\_ID": "{env:QUANTCONNECT\_ORGANIZATION\_ID}"
    }
  }
}

Steps to Reproduce

Start the QuantConnect MCP server via Docker, either via the MCP host using the config above, or manually with: docker run -it --rm \
-e QUANTCONNECT_USER_ID=YOUR_ID \
-e QUANTCONNECT_API_TOKEN=YOUR_TOKEN \
-e QUANTCONNECT_ORGANIZATION_ID=YOUR_ORG \
mcp/quantconnect

From the MCP client, call the list_backtests tool for a project that has existing backtests (for example, project ID PROJECT_ID_HERE).
Observe the tool failure in the client logs.

Actual Behavior
The tool call fails with Pydantic validation errors. Exact error from the client:
Error executing tool list_backtests: 88 validation errors for BacktestSummaryResponse
backtests.0.parameterSet.ParameterSet1
Input should be a valid dictionary or instance of ParameterSet1 [type=model_type, input_value=[], input_type=list]
backtests.0.parameterSet.dict[str,union[str,float,int]]
Input should be a valid dictionary [type=dict_type, input_value=[], input_type=list]
[... similar errors for backtests 1-43 ...]
The server successfully retrieved 44 backtests (IDs 0-43), but cannot deserialize the parameterSet field for any of them due to malformed data format in the API response.

From this it appears:
The QuantConnect API (or MCP bridge) is returning parameterSet: [] for each backtest.
The MCP Pydantic model expects parameterSet to be a dict[str, Union[str, float, int]] (or ParameterSet1), so an empty list fails validation.
Expected Behavior
Either:
parameterSet should be returned as {} (an empty dict) when there are no parameters, or
The MCP model should accept list/None for empty parameterSet values.
list_backtests should succeed and return the list of backtests even when they have no parameters.
Additional Notes
The server does successfully fetch 44 backtests; only deserialization of parameterSet fails.
Pulling mcp/quantconnect:latest again confirms the image is up to date; the issue persists.

Happy to provide more logs or try a patched image if needed.

[npschweizer]

Hi All, is there any other information you're missing?