ZeroServer.tools

CORS Header Generator

Build Cross-Origin Resource Sharing headers for Express, nginx, Apache, or raw HTTP.

Allow-Origin

Credentials

Allow-Methods (comma-separated)

Allow-Headers (comma-separated)

Max-Age (preflight cache)

Expose-Headers

Output format

Generated output

Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET,POST
Access-Control-Allow-Headers: Content-Type,Authorization
Access-Control-Max-Age: 86400

How CORS headers work

Cross-Origin Resource Sharing (CORS) is a browser security mechanism that controls which origins can call your API. The server responds with Access-Control-Allow-Origin to approve or reject the request. For pre-flight requests (OPTIONS), the browser also checks Access-Control-Allow-Methods and Access-Control-Allow-Headers. Setting Access-Control-Max-Age caches the pre-flight result to reduce extra round-trips.

Never set Access-Control-Allow-Origin: * combined with Access-Control-Allow-Credentials: true — browsers will reject it.

Private & free — this tool runs entirely in your browser.