MCP server keep loading and display error: Invalid URL protocol

Bug Reports
1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

I added mcp server setting:

{
  "mcpServers": {
    "Figma": {
      "url": "https://mcp.figma.com/mcp"
    }
  }
}

Then the mcp server state becomes “Loading tools” and here is the log

2025-10-24 17:44:29.152 [info] No stored tokens found
2025-10-24 17:44:29.152 [error] Client error for command SSE error: Invalid URL protocol: the URL must start with http: or https:.
2025-10-24 17:44:29.152 [error] Error connecting to SSE server after fallback: SSE error: Invalid URL protocol: the URL must start with http: or https:.

Steps to Reproduce

Set

{
  "mcpServers": {
    "Figma": {
      "url": "https://mcp.figma.com/mcp",
      "headers": {}
    }
  }
}

Expected Behavior

Go on and show something else instead of showing the URL error

Operating System

MacOS

Current Cursor Version (Menu → About Cursor → Copy)

Version: 1.7.54
VSCode Version: 1.99.3
Commit: 5c17eb2968a37f66bc6662f48d6356a100b67be0
Date: 2025-10-21T19:07:38.476Z (2 days ago)
Electron: 34.5.8
Chromium: 132.0.6834.210
Node.js: 20.19.1
V8: 13.2.152.41-electron.0
OS: Darwin arm64 23.4.0

Does this stop you from using Cursor

Sometimes - I can sometimes use Cursor

2

Hey, thanks for the report. The issue is with the Figma MCP setup.

Figma MCP runs locally, not via a direct remote URL. You need to:

  1. Follow Figma’s instructions to start the local server: Guide to the Figma MCP server – Figma Learn - Help Center
  2. Update your mcp.json configuration:
{
  "mcpServers": {
    "Figma": {
      "url": "http://127.0.0.1:3845/sse"
    }
  }
}

The error indicates that the URL https://mcp.figma.com/mcp isn’t recognized by Cursor’s MCP client as a valid SSE endpoint.

If the local Figma server is already running but the issue persists, please share the full MCP logs (Output tab → select “MCP: Figma” in the dropdown).

Let me know if this helps.

3

So is it depends on the MCP server’s response?

Now my another MCP server also faces this problem
```
{

“mcpServers”: {

“ai-sdk-5-migration”: {

“url”: “https://ai-sdk-5-migration-mcp-server.vercel.app/api/mcp”

}

}

}
```

4

Got it, thanks. The error points to URL protocol validation failing, even though your URLs look correct.

For the ai-sdk-5-migration server (https://ai-sdk-5-migration-mcp-server.vercel.app/api/mcp): the JSON‑RPC error confirms it’s not an SSE server, it’s a standard JSON‑RPC endpoint.

Cursor’s MCP client supports remote servers over SSE only. SSE streams events via GET, while your Vercel endpoint responds with JSON‑RPC (typically POST).

Solutions:

  • Check if the ai-sdk-5-migration MCP server documents an SSE endpoint
  • If it only supports STDIO/JSON‑RPC, run it locally via a command instead of using a URL
  • Use a different MCP server that supports SSE for remote connections

Same for Figma, their MCP runs locally via stdio, which is why a local bridge at http://127.0.0.1:3845/sse works (it translates to SSE).

5

Thanks, but this is my another cursor account. The same confiuration works on this version of Cursor.

image
image2272×1058 185 KB

And here is the version:

Version: 1.7.46
VSCode Version: 1.99.3
Commit: b9e5948c1ad20443a5cecba6b84a3c9b99d62580
Date: 2025-10-14T01:21:46.830Z (1 wk ago)
Electron: 34.5.8
Chromium: 132.0.6834.210
Node.js: 20.19.1
V8: 13.2.152.41-electron.0
OS: Darwin arm64 23.6.0

Both use HTTP/1.1 as HTTP compatibility mode.

I feel like this is a bug of the latest version IDE

6

Thanks for the info, we’ll look into it. Also please update to version 1.7.54 and let me know if the issue still persists.

7

Actually, the latest 1.7.54 is the faulty version

1 Like