Cross-Origin Resource Sharing (CORS) Header Rule Builder
Build production Access-Control-Allow headers, preflight OPTIONS handlers, and Nginx/Next.js configs.
Execution runs 100% locally inside the browser sandbox using HTML5 Canvas, Web Cryptography Subtle API, and Web Workers. No data is ever transmitted across the network.
Zero network latency. Operates completely offline with zero dependencies on third-party backend servers or cloud services.
Built according to official RFC specifications, cryptographic test vectors, and enterprise-grade data transformation standards.
How to Use Cross-Origin Resource Sharing (CORS) Header Rule Builder
Enter your frontend domain origin (e.g. https://app.example.com).
Choose allowed HTTP verbs and request headers.
Copy the raw HTTP headers or web server blocks.
Frequently Asked Questions
Why avoid Access-Control-Allow-Origin: * with credentials?
Browsers strictly reject credentials (cookies/auth) if Access-Control-Allow-Origin is set to wildcard *.
What is Access-Control-Max-Age?
It caches preflight OPTIONS responses in client browsers to reduce redundant network round trips.
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