MCP error on add entity

[Anton_L]

Hello!

I installed in Cursor editor-mcp-server GitHub - playcanvas/editor-mcp-server: MCP Server for AI automation of the PlayCanvas Editor.

Operating system: Windows 10.

Calling through Cursor.

Works great on questions like: show or tell about something on a scene in the browser. But as soon as I ask to create something, it gives an error like: The model returned an error. Try disabling the MCP servers or switching the model. Despite the error, the object I asked to create appears in the scene.

Could someone please tell me if it is possible to fix this?

Thanks in advance for the answer!

[mvaligursky]

@KPal

[will]

Hi! It looks like you have the LLM set to Auto. The MCP Serer only works with Claude Sonnet at the moment (both 3.5 and 3.7 should work. So please explicitly select one of those.

But note that the PlayCanvas MCP Server does require a reasonable size chat context. So if you get errors about that in Cursor, perhaps the paid (MAX) flavor of Claude Sonnet would fix that. Personally, I use Claude Desktop (with a Pro account) and that works perfectly.

Let me know how you get on! (And by the way, I upgraded the MCP Server quite significantly on the weekend, so do get latest and read the GitHub repo README which has been updated regarding the latest version of the Chrome extension that now requires you to explicitly connect to the Server from the Editor tab).

[Anton_L]

Thanks for the reply!

Changes pulled, browser extension activated.

I removed the auto model selection on Claude 3.5 and 3.7. But unfortunately that didn’t solve the situation. Maybe the problem is in the Cursor itself

[Anton_L]

I also connected MCP Playcanvas in Windsurf. As a result, it gives an error that the MCP server gave an invalid JSON Schema, which Windsurf can’t parse - it expected an object {}, but got an array .

And he complains about the create_entities tool, which was causing errors when I asked the neural network to create something.

There was no detailed error in Cursor.

[Anton_L]

I also installed Claude Desktop with the free plan.

Do I understand correctly that all the MCP server tools generate a request so large that it exceeds the base request limit in the free Claude plan?

[will]

That’s my very strong suspicion, yes. I have no problems on the Pro plan.

[Edward_Wang]

I got the same issue on both Cursor and Windsurf, all same as yours, how to fix that??

[will]

@Edward_Wang As I say, I have only had success using the PlayCanvas MCP Server with Claude Desktop with a Pro plan activated.

[blindbenfilms]

Hello!

I’m using the PlayCanvas MCP Server with Claude Desktop Pro on Windows, and I’m experiencing issues with write operations after trying all troubleshooting steps.

My Setup:

• Windows PC
• Claude Desktop with active Pro subscription (monthly plan)
• Node.js and npm installed
• PlayCanvas Editor MCP Extension v1.1.26 installed
• MCP Server location: C:\Users\Ben Fox\Documents\editor-mcp-server-main
• Chrome extension shows “CONNECTED”
• Claude Desktop shows playcanvas as “running”

Config File (Windows format with cmd /c):

json

{
  "mcpServers": {
    "playcanvas": {
      "command": "cmd",
      "args": [
        "/c",
        "npx",
        "tsx",
        "C:\\Users\\Ben Fox\\Documents\\editor-mcp-server-main\\src\\server.ts"
      ],
      "env": {
        "PORT": "52000"
      }
    }
  }
}

What Works:

• playcanvas:list_entities - works perfectly
• playcanvas:query_scene_settings - works perfectly
• All read operations succeed consistently

What Fails:

• playcanvas:create_entities - returns “Tool execution failed”
• playcanvas:modify_entities - returns “Tool execution failed”
• playcanvas:duplicate_entities - returns “Tool execution failed”
• playcanvas:create_assets - returns “Tool execution failed”
• All write operations fail with no additional error details

Console Output (stable connection):

[WSC] Connecting to ws://localhost:52000
[WSC] Connected

Connection remains stable with no disconnects.

Troubleshooting Already Completed:

• Upgraded to Claude Pro subscription
• Tried both with and without cmd /c in config
• Ensured no manual Command Prompt server running (port conflict)
• Restarted Claude Desktop multiple times
• Reconnected Chrome extension multiple times
• Verified WebSocket stays connected (no disconnects)
• Confirmed npm install completed successfully

The WebSocket connection is healthy and stable, read operations work flawlessly, but all write operations fail silently with just “Tool execution failed” and no detailed error messages.

Question: Is this a known issue with the current version? Are there any additional configuration steps or permissions needed for write operations to work on Windows with Claude Desktop Pro?

Any help would be greatly appreciated! I’m excited to use this for an accessibility-focused art gallery project.

Thanks in advance! Ben Fox

[mvaligursky]

@KPal might know

[blindbenfilms]

Is it possible to hire a specialist to help me with this setup of the MCP?