CORS Tester Online Free
Test any URL or API endpoint for Cross-Origin Resource Sharing (CORS) headers, preflight OPTIONS requests, and origin permissions.
How to Use CORS Tester
Configure Input & Parameters
Enter your target endpoint, pattern, or data payload in the input fields above.
Execute Real-Time Analysis
Click the action button or type to trigger client-side validation, testing, and processing instantly.
Inspect & Export Results
Review detailed status badges, response trees, and copy formatted output to your clipboard.
Frequently Asked Questions
What is CORS?
Cross-Origin Resource Sharing (CORS) is a browser security mechanism that uses HTTP headers to allow or restrict resources requested from another domain.
Why does my fetch request fail in JavaScript?
If the destination server does not return the `Access-Control-Allow-Origin` header matching your website domain, modern web browsers block client-side JavaScript from reading the response.
100% Client-Side Privacy
All tests, tokens, queries, and payload processing run securely inside your browser. No sensitive credentials or data ever hit external servers.
Explore More Free Image Tools
Fast, 100% private in-browser tools for converting, compressing, resizing, cropping, and optimizing images.
All Tools Directory - 241+ Free Tools
Complete suite of private image processors, PDF utilities, and YouTube creator tools.