CORS: Browser Cross-Origin Request Debugging
Cross-Origin Resource Sharing (CORS) manages how browsers restrict client-side scripts from accessing resources on other origins. Explore practical guides for diagnosing CORS headers, preflight requests, and common cross-origin failures.
Articles & Guides
API Works in Postman but Not in Browser? Fix CORS
Learn why an API can work in Postman but fail in browser JavaScript, how CORS preflight works, and how to verify the real cause.
Authorization Header Is Not Allowed by CORS
Learn why the Authorization header triggers a CORS preflight error, why servers must explicitly allow it, and how to diagnose the issue in DevTools.
CORS Error or HTTP 401/403/500? How CORS Can Hide API Errors
Discover why CORS errors often mask underlying HTTP 401, 403, or 500 status codes, and how to uncover the real server response in browser DevTools.
CORS Preflight Request Failing: OPTIONS, 401, 403, 404, and 405
Diagnose why an OPTIONS preflight request fails with 401, 403, 404, or 405 status codes, and how to verify preflight CORS headers and routing.
No Access-Control-Allow-Origin Header: Causes and Fixes
Learn why the Access-Control-Allow-Origin header is missing from API responses, why Postman works while browsers fail, and how to safely resolve it.
What Is CORS? A Practical HTTP Guide
Understand Cross-Origin Resource Sharing (CORS), how browser Same-Origin Policy works, what CORS headers do, and how cross-origin requests are handled.
Why Access-Control-Allow-Origin Wildcard Fails with Credentials
Understand why Access-Control-Allow-Origin: * fails when requests include credentials (cookies, auth), and how to configure explicit origins safely.
Why Does the Browser Send an OPTIONS Preflight Request?
Understand why web browsers send an automatic OPTIONS preflight request before certain cross-origin HTTP calls and how preflight headers work.
Debugging Browser CORS Restrictions
When troubleshooting CORS failures, inspect the browser DevTools Network panel to identify whether the issue is a missing response header, a failing preflight request, or an origin mismatch.