📖 CORS Handbook#

The complete guide to understanding and fixing CORS errors.

Cross-Origin Resource Sharing doesn’t have to be confusing. Whether you’re seeing your first CORS error or debugging a complex preflight issue, we’ve got you covered.

🔥 Most Popular#

• What Is CORS and Why Is It Ruining Your API Calls? — Start here if you’re new to CORS
• The 7 CORS Errors You’ll See Most — Copy-paste fixes for common errors

📚 By Topic#

Understanding CORS#

• What Is CORS? — How CORS works and why browsers block your requests
• CORS vs Same-Origin Policy — The difference everyone confuses
• Preflight Requests Explained — Why the browser sends two requests

Fixing CORS Errors#

• Fix the 7 Most Common CORS Errors — Specific solutions for each error
• Every CORS Header Explained — Complete header reference with examples

By Server#

• CORS in Node.js and Express — From basic to production-ready
• CORS in Nginx and Apache — Production-ready server configurations

🧪 Test Your Headers#

Check your CORS configuration with headertest.com — free, no signup required.