Why am I getting CORS errors even though my server returns 200?

The browser blocks the response if CORS headers are missing or incorrect. The server must return Access-Control-Allow-Origin and handle OPTIONS preflight requests.

How do I fix CORS on Express?

Install the cors package and add app.use(cors({ origin: 'your-frontend.com' })). CORSFixer generates the exact config based on your live preflight response.

Can I use Access-Control-Allow-Origin: * with credentials?

No — browsers reject this combination per the CORS spec. You must specify an explicit origin when using credentials: true.

#1 developer rage-quit. CORSFixer finds exactly why your CORS is broken — and generates the middleware fix for your framework.

Tests your real CORS configuration with a live OPTIONS preflight. Generates fixes for Express, Nginx, FastAPI, Django, Laravel, and Cloudflare Workers.

Target URL

Request Origin

Your URL never leaves your browser — this is a live client-side preflight

Tip: curl -sI -X OPTIONS https://api.your-domain.com -H "Origin: https://your-frontend.com"

Request origin (for fix generation)

Detected framework: