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ChatGPT MCP Setup Guide

Complete guide to connect your Plaid MCP server to ChatGPT using OAuth 2.1.

Prerequisites

  1. ✅ ChatGPT Plus or Pro subscription
  2. ✅ Plaid MCP server built and configured
  3. ✅ ngrok or public HTTPS URL
  4. ✅ OAuth credentials generated in .env.local

Quick Start

Step 1: Start Your Server

# Build the server
npm run build

# Start the SSE server
npm run start:sse

You should see:

🔒 OAuth 2.1 authentication enabled (with PKCE and Dynamic Client Registration)
Plaid MCP SSE Server running on http://localhost:3001

Step 2: Expose with ngrok

In a new terminal:

ngrok http 3001

You'll get an HTTPS URL like: https://abc123.ngrok-free.dev

⚠️ Important: ChatGPT requires HTTPS - don't use the HTTP URL!

Step 3: Get Your OAuth Credentials

cat .env.local | grep MCP_OAUTH

Example output:

MCP_OAUTH_CLIENT_ID=f14a6478125f6698
MCP_OAUTH_CLIENT_SECRET=647ff36aead390189890fe13f93a7caf

Step 4: Add to ChatGPT

  1. Open ChatGPT → Settings → Connectors
  2. Click "Add Connector"
  3. Fill in the details:
Field Value Example
Name Plaid Banking (any name)
MCP Server URL https://YOUR-NGROK-URL.ngrok-free.dev ⚠️ NO /sse suffix!
Authentication OAuth (select from dropdown)
OAuth Client ID From .env.local f14a6478125f6698
OAuth Client Secret From .env.local 647ff36aead390189890fe13f93a7caf
  1. Click "Create"

Step 5: Authorize Access

  • A browser window will open automatically
  • You'll see an authorization consent screen
  • Review the permissions:
    • Access your Plaid banking data
    • Execute MCP tools on your behalf
    • Manage your connected accounts
  • Click "Authorize"

✅ ChatGPT will complete the connection and show the connector as "Connected"!

Available Tools

Once connected, try asking ChatGPT:

  • "List my connected Plaid items"
  • "Show me my account balances"
  • "Get my transactions from last month"
  • "Create a link token to connect my bank"

See README.md for the complete tool list.

How It Works

The OAuth 2.1 flow with PKCE:

  1. Discovery - ChatGPT finds your OAuth endpoints
  2. Registration - ChatGPT registers using provided credentials
  3. Authorization - You approve access in browser
  4. Token Exchange - ChatGPT exchanges code for access token
  5. Authenticated Requests - All MCP requests include the token

Troubleshooting

"Error fetching OAuth configuration"

Problem: ChatGPT can't find OAuth endpoints

Solution:

# Test that discovery endpoints work
curl https://YOUR-NGROK-URL/.well-known/oauth-authorization-server

# Should return JSON with authorization_endpoint, token_endpoint, etc.
# NOT a 404 or 401 error

"Invalid client_id" in browser

Problem: OAuth credentials don't match

Solution:

  1. Check credentials in .env.local match ChatGPT exactly
  2. Restart server after changing .env.local: 
    pkill -f sse-server
npm run start:sse

Authorization page hangs

Problem: Redirect back to ChatGPT fails

Solution:

  1. Check server logs for errors
  2. Verify ngrok is still running
  3. Try deleting and re-adding the connector in ChatGPT

ngrok URL changed

Problem: Connection stopped after restarting ngrok

Solution:

  1. Get new URL: check ngrok terminal
  2. In ChatGPT: Delete old connector
  3. Add new connector with new URL
  4. Use same OAuth credentials (no need to regenerate)

Connection works but tools don't appear

Problem: ChatGPT shows "Connected" but no tools

Solution:

  1. Check server logs for SSE connection
  2. Try asking ChatGPT: "What MCP tools do you have access to?"
  3. Refresh ChatGPT page

Testing Before ChatGPT

Verify your setup works:

# 1. Test OAuth discovery (public - no auth needed)
curl https://YOUR-NGROK-URL/.well-known/oauth-authorization-server | jq .

# Should show: authorization_endpoint, token_endpoint, registration_endpoint

# 2. Test server health
curl https://YOUR-NGROK-URL/health | jq .

# Should show: status: "ok", authentication: "oauth2.1"

# 3. Test with automated client (local only)
npm run test

Note: npm run test starts a temporary test server with authentication bypassed. It only works for local testing and will temporarily stop your production server on port 3001.

Server Logs

Monitor your server in real-time:

# Follow server logs
tail -f /tmp/sse-server.log

# Look for these successful events:
# 🔐 OAuth authorization request from client: ...
# ✅ Authorization code issued
# 🎫 OAuth token request
# ✅ Access token issued
# ✅ Authenticated OAuth request

Security Notes

  • 🔒 Uses OAuth 2.1 with PKCE (Proof Key for Code Exchange)
  • 🔒 Access tokens expire after 1 hour
  • 🔒 Authorization codes are single-use and expire in 10 minutes
  • 🔒 All tokens stored in memory (cleared on restart)
  • 🔒 HTTPS required (ngrok provides this automatically)
  • 🔒 Never commit .env.local to git

Production Deployment

For production use:

  1. Deploy to a server with a stable HTTPS URL (not ngrok)
  2. Generate new OAuth credentials for production
  3. Set up proper token storage (Redis/database instead of memory)
  4. Add rate limiting and request logging
  5. Monitor OAuth flows for security issues

See DEPLOYMENT.md for detailed production setup.

Next Steps

Once connected successfully:

  1. Connect a bank: "Create a link token to connect my bank account"
  2. View data: "Show me my account balances"
  3. Analyze spending: "Get my transactions from last month and categorize them"
  4. Find subscriptions: "Find all my recurring transactions"

Enjoy using your Plaid banking data with ChatGPT! 🎉