First two MCP app extension examples in mcp official doc (map and threejs) fail to run

[Chenxi_Shi]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

See image below

Steps to Reproduce

install mcp and ask question

{
    "mcpServers": {
        "map": {
            "command": "npx",
            "args": [
                "-y",
                "--silent",
                "--registry=https://registry.npmjs.org/",
                "@modelcontextprotocol/server-map",
                "--stdio"
            ]
        },
        "threejs": {
            "command": "npx",
            "args": [
                "-y",
                "--silent",
                "--registry=https://registry.npmjs.org/",
                "@modelcontextprotocol/server-threejs",
                "--stdio"
            ]
        }
    }
}

Screenshots / Screen Recordings

Operating System

MacOS

Version Information

Version: 2.6.18 (Universal)

For AI issues: which model did you use?

opus 4.6

Does this stop you from using Cursor

No - Cursor works, but with this issue

[deanrie]

Hey, thanks for the report.

Both MCP servers do start, and the tools run successfully (“Ran Show Map in map”, “Ran Show Threejs Scene in threejs”). The issue is that CesiumJS and Three.js rely on dynamic JavaScript execution (eval() or new Function()), which is currently restricted in the MCP Apps rendering environment. That is what the red error is about.

This is a known limitation on our side. I shared it with the team. There is no ETA yet, but your report helps us prioritize it.

Unfortunately, there is no workaround right now. I will update this thread if anything changes.

[Chenxi_Shi]

Is Cursor going to adapt to fully support MCP, or will MCP start constraining dynamic JS?

[deanrie]

This is a limitation on our side. We’re tracking it, but there’s no timeline yet. I’ll update this thread if anything changes.