📖 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.

The 7 CORS Errors You'll See Most (And Exactly How to Fix Each One)

I’ve fixed more CORS errors than I can count. They all look slightly different but most fall into the same handful of categories. Here are the seven you’ll see most often, with the exact fix for each. Error 1: “No ‘Access-Control-Allow-Origin’ header is present” Access to fetch at 'https://api.example.com/users' from origin 'https://myapp.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. This is the most common CORS error. It means your server isn’t sending any CORS headers at all. ...

What Is CORS and Why Is It Ruining Your API Calls?

You’ve built a React frontend. You’ve built a Node.js API. They work perfectly when you test them separately. You wire them together, make your first API call, and… Access to fetch at 'http://localhost:3001/api/users' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Sound familiar? Every developer hits this wall. And most developers respond by Googling “how to fix CORS” and pasting app.use(cors()) without understanding what they just did. ...

📖 CORS Handbook#

🔥 Most Popular#

📚 By Topic#

Understanding CORS#

Fixing CORS Errors#

By Server#

🧪 Test Your Headers#