Gabriel Alejandro Garcia

Posted on Feb 6

How to Connect MercadoLibre MCP in Antigravity/Cursor: The Missing Guide

#mercadolibre #mcp #antigravity

If you are using Antigravity (or Cursor) as your AI-native IDE, you might have noticed that the official MercadoLibre developers documentation haven't caught up with these tools yet. Setting up the Model Context Protocol (MCP) for MeLi can be tricky due to specific port requirements and OAuth flows.

After a long troubleshooting session, I've cracked the code on how to get it working perfectly. Here is the definitive guide for Antigravity users.

1. The "Application Not Ready" Error

The most common issue: you authorize in the browser, but the page says:

"La aplicación no está preparada para conectarse a Mercado Libre"

The Problem

The official MeLi MCP proxy app strictly expects a redirect to http://localhost:18999. However, the mcp-remote client used by IDEs like Antigravity often picks a random port (like 17135) if not told otherwise.

The Fix: Force Port 18999

In your mcp_config.json (usually in %APPDATA%\.gemini\antigravity\), you must add 18999 as a positional argument.

"mercadolibre": {
  "command": "npx",
  "args": [
    "-y",
    "mcp-remote",
    "https://mcp.mercadolibre.com/mcp",
    "18999"  // <-- REQUIRED for MeLi compatibility
  ],
  "disabled": false
}

2. Eliminate Conflict: Remove Manual Headers

If you previously tried to add a token manually, delete it. You cannot use a hardcoded Bearer token while using the OAuth browser flow.

[!WARNING]
Remove the following lines from your mcp_config.json:
"--header",
"Authorization: Bearer APP_USR-..."

Keeping these while trying to log in via browser will cause the authentication exchange to fail with "Existing OAuth client information is required".

3. Resolving Port Conflicts (EADDRINUSE)

If you get an error saying address already in use 127.0.0.1:18999, it means a previous (failed) attempt left a "zombie" process running.

Windows Recovery (PowerShell):

Kill all Node.js zombies:

   taskkill /F /IM node.exe

Clear the corrupt auth cache:

   rmdir /S /Q $HOME\.mcp-auth

4. Final Tips for Antigravity/Cursor Users

Browser Specifics: If Firefox is your default browser and the "Authorization Successful" page doesn't seem to talk back to your IDE, copy and paste the link into Chrome. It often handles the local callback more reliably for dev tools.
Beat the Timeout: Antigravity has a built-in timeout. Once the browser opens, complete the authorization quickly. If it fails, you'll see a context deadline exceeded error.
Ngrok?: You don't need Ngrok for this setup. The MeLi MCP Proxy is an official app that already has permission to talk to your localhost:18999.

Summary

Force 18999 in your config.
Remove any manual headers.
Clear zombie node processes.
Use Chrome if the callback fails.

Happy AI-Coding! 🚀

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