CORS Headers Explained
All-in-one resource for understanding CORS headers, including usage, common errors and code examples. Perfect for web developers and API makers.
Access-Control-Allow-Origin
Define which origins are allowed to access cross-origin resources.
Access-Control-Allow-Credentials
Determine if credentials (cookies, authentication headers) can be included.
Access-Control-Allow-Headers
Specify which headers clients can use in cross-origin requests.
Access-Control-Allow-Methods
Specify which HTTP methods are allowed in cross-origin requests.
Access-Control-Expose-Headers
Enable client-side JavaScript to read non-standard response headers.
Access-Control-Max-Age
Reduce latency by caching preflight results for faster requests.
Access-Control-Request-Headers
Lists the headers the client intends to send with the actual request.
Access-Control-Request-Method
Specifies the HTTP method the client plans to use in the actual request.
Origin
Indicates where the request originated from (scheme, hostname, port).
When do these headers matter?
For Web Developers
Understand CORS to troubleshoot and fix issues when your frontend application interacts with APIs on different origins.
For API Makers
Learn how to configure CORS headers to securely enable client-side access to your API from various origins.
Explore More Tools
CORS Tester
Paste any API endpoint and instantly see if it supports CORS and which headers it returns.
Try the testerCORS Proxy Playground
Bypass CORS errors in your web app by routing your requests through our CORS proxy.
Open playground