unknown MCP

[shlypa100-maker]

Hello! I’ve encountered a problem when using Unity-MCP with the Cursor (and Codex) MCP clients.

Unity-MCP is installed correctly and shows “Connected” inside the Unity AI Game Developer window. Tools are successfully detected by Cursor, but when any tool is executed, the client throws the following error:

MCP error -32602: Structured content does not match the tool's output schema: data.result should be string

It seems that the structuredContent returned by the Unity-MCP server does not fully match the outputSchema expected by the MCP client. Cursor performs strict JSON schema validation and fails when “result” is not a string or when the server returns fields not defined in the schema.

Environment:

• Unity-MCP version: 0.22.0
• OS: Windows 11
• Client: Cursor (latest version)
• Server: Unity-MCP (launched via auto-generated configuration)
• Connection status in Unity: “Connected” (green)

Reproduction:

1. Install Unity-MCP using OpenUPM.
2. Connect to MCP server in Unity.
3. Configure Cursor using the JSON provided in the “Manual Configuration” section.
4. Cursor detects all Unity-MCP tools.
5. Execute any tool (e.g. get_scene_hierarchy, create_gameobject).
6. Cursor throws the error:

Structured content does not match the tool's output schema: data.result should be string

Notes:

• Claude Code and Claude Desktop work without this issue (they are less strict).
• Cursor and Codex use strict schema validation for structuredContent.
• Unity-MCP appears to return a response object that does not fully match the schema declared for each tool.

Expected:
Tool outputs should match the declared outputSchema exactly, so strict MCP clients like Cursor/Codex can validate them successfully.

Thank you for your work on this project!

[IvanMurzak]

Thank you for the report. It is a new but already known problem. Your report is helpful anyway because it provides well detailed information.
There are 42 tools, seems like some of them have a difference between real output and json schema.

If you know which exact tool provides incorrect format - that would be even more helpful. Anyway, I will do my own investigation and the fix of the problem.

[IvanMurzak]

@shlypa100-maker I made the fix at least of some of the tools.
The fix was done here: #313
And right now it is available in the version 0.22.1.

Please let me know if you find a tool which still provide incorrect structured content. And please keep your eye on the tool name, it would help to fix it.