Empty Input Schema Breaks Copilot CLI

[IvanMurzak]

Describe the bug

Tools with no input parameters use an empty JSON Schema for their Input Schema. This causes Copilot CLI to reject the tool entirely and fail on any prompt when the MCP server is connected.

Error from Copilot CLI:

✘ Model call failed: {"message":"Invalid schema for function 'ai-game-developer-assets-prefab-save':
  In context=(), object schema missing properties.","code":"invalid_function_parameters"}
  (Request ID: D7FC:AD056:2DA15A3:3398963:69A8149D)

Affected version

0.0.365 Commit: 76d0881

Steps to reproduce the behavior

1. To have an MCP tool with this Input Schema:

{
  "type": "object",
  "additionalProperties": false
}

2. Start copilot.
3. Type any prompt when connected to the MCP with the tool.

Result

Copilot is stuck producing this error again and again. Nothing else happens, doesn't matter what prompt to type. Only adding an input argument into the input json schema of the tool resolves the problem.

Sample (functional Input Schema)

{
  "type": "object",
  "properties": {
    "dummy": {
      "type": "string"
    }
  },
  "required": ["dummy"]
}

Expected behavior

Copilot doesn't have the error about MCP tool with no arguments and can continue to operate and use it.

Additional context

Seems like Copilot CLI requires every object schema to have a properties field. An empty object schema (with only additionalProperties: false and no properties) is rejected as invalid.

[AndrewBert]

Yes same here would love a fix!

[copilot-cli-bot]

This appears to be resolved as of GitHub Copilot CLI v1.0.89. Please update to that release or a newer stable version. We're closing this as completed. If it still happens, please comment with your version and reproduction steps.