CORS Access-Control Header Generator

CORS DIRECTIVES CONFIGURATION

Allowed Origin (Access-Control-Allow-Origin)

Allowed Methods (Access-Control-Allow-Methods)

Allowed Headers (Access-Control-Allow-Headers)

Allow Credentials (Access-Control-Allow-Credentials: true)

GENERATED CORS HEADER RESPONSE

HTTP Headers Block

Express.js Middleware Snippet

CORS Security Configuration Guide — Safe API Endpoint Sharing

Cross-Origin Resource Sharing governs how web browsers make cross-domain HTTP requests. Proper CORS header configuration prevents unauthorized domain access while allowing legitimate frontend clients to communicate with API servers.

Key Access-Control Headers

Access-Control-Allow-Origin — Specifies authorized client domains.
Access-Control-Allow-Methods — Lists allowed HTTP methods (GET, POST, OPTIONS).
Access-Control-Allow-Headers — Specifies allowed custom request headers.
Access-Control-Max-Age — Caches preflight OPTIONS check duration.

Related Security Tools

Generate CSP headers with the CSP Header Generator, enforce HSTS with the HSTS Header Generator, or test JWT tokens with the JWT Inspector.

Frequently Asked Questions

Common questions about this tool.

What is CORS (Cross-Origin Resource Sharing)? ▼

CORS is an HTTP-header-based mechanism that allows a server to indicate any origins (domain, scheme, or port) other than its own from which a browser should permit loading resources.

Why is `Access-Control-Allow-Origin: *` dangerous for authenticated APIs? ▼

Using wildcard `*` with credentials (`Access-Control-Allow-Credentials: true`) is rejected by browsers and can expose sensitive user session data to third-party domains.

What is a CORS preflight OPTIONS request? ▼

A preflight request is an automatic `OPTIONS` HTTP request sent by browsers before non-simple requests (like `POST` with `Content-Type: application/json` or custom authorization headers).

How do I allow multiple specific domains in CORS? ▼

Inspect the incoming `Origin` HTTP request header dynamically in your server code or Nginx map block, returning that origin if it matches your whitelist.

What is `Access-Control-Max-Age`? ▼

`Access-Control-Max-Age` specifies how many seconds preflight OPTIONS request results can be cached by browsers (e.g. `86400` for 24 hours), reducing API round-trips.