CORS Header Generator
Visually configure CORS headers and get copy-paste-ready configuration for Nginx, Apache, and Express.js.
How ZeroData protects your privacy
- ✓ No Uploads: Processing happens entirely via client-side JavaScript.
- ✓ No Storage: We do not have a database. We physically cannot save your data.
- ✓ No Tracking: We don't log what you process or track your inputs.
- ✓ Verifiable: Check your DevTools Network tab. You will see 0 outbound requests.
Stop Guessing CORS Headers
CORS errors are one of the most common — and most frustrating — issues in web development. The dreaded "Access to XMLHttpRequest has been blocked by CORS policy" message has cost developers millions of hours of debugging time.
The problem is that CORS configuration is spread across different syntaxes depending on your server: Nginx uses add_header, Apache uses Header set in .htaccess, and Express.js uses middleware. Each has slightly different formatting rules, and a single typo means the headers won't work.
This CORS Header Generator gives you a visual form where you select your allowed origins, HTTP methods, headers, and credential settings. It then generates the exact configuration for Nginx, Apache, Express.js, and raw HTTP headers — all ready to copy and paste directly into your server config.
Want to verify your CORS headers are working correctly? Use our CORS Tester to send real requests from your browser and check the response headers. For a complete understanding of CORS mechanics, read our guide to fixing common CORS errors.
Common Use Cases
- Configuring CORS headers for a new REST API that serves a React/Vue/Angular frontend.
- Fixing 'Access to XMLHttpRequest has been blocked by CORS policy' errors.
- Setting up Nginx reverse proxy CORS headers for a microservices architecture.
- Generating Apache .htaccess rules for cross-origin resource sharing.
- Adding CORS middleware to an Express.js or Node.js backend.
Frequently Asked Questions
What is CORS and why do I need it?
CORS (Cross-Origin Resource Sharing) is a browser security mechanism that blocks web pages from making requests to a different domain than the one that served the page. If your frontend (e.g., app.example.com) calls an API on api.example.com, the API server must include CORS headers to allow the request.
What does Access-Control-Allow-Origin: * mean?
The wildcard (*) means any website in the world can call your API. This is fine for public APIs with no authentication, but dangerous for private APIs. If you use credentials (cookies/tokens), you MUST specify exact origins instead of *.
Why do I see a preflight OPTIONS request?
Browsers send a 'preflight' OPTIONS request before certain cross-origin requests (those with custom headers, PUT/DELETE methods, etc.) to check if the server allows it. Your server must respond to OPTIONS requests with the correct CORS headers and a 204 status code.
Can I use Allow-Credentials with wildcard origin?
No. Browsers explicitly block Access-Control-Allow-Credentials: true when the origin is set to *. You must specify the exact origin domain(s) when using credentials.
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