CORS is an HTTP-header based security mechanism enforced by web browsers to restrict cross-origin network requests from accessing sensitive server resources.
Cross-Origin Resource Sharing (CORS) is a W3C and WHATWG browser security standard that uses HTTP headers to tell browsers whether a web application running at one origin (protocol, domain, port) has permission to access resources from a server at a different origin.
Inspect HTTP response headers with the HTTP Headers Analyzer, test preflight OPTIONS requests in the API Request Builder, or convert cURL commands into browser fetch scripts with the cURL Converter.
| Header | Purpose | Example |
|---|---|---|
Access-Control-Allow-Origin |
Specifies authorized origin(s) | https://app.example.com or * |
Access-Control-Allow-Methods |
Allowed HTTP methods | GET, POST, PUT, DELETE, OPTIONS |
Access-Control-Allow-Headers |
Allowed request headers | Content-Type, Authorization, X-Requested-With |
Access-Control-Allow-Credentials |
Permits cookies & Authorization headers | true |
Access-Control-Max-Age |
Preflight cache lifetime in seconds | 86400 (24 hours) |
OPTIONS)When an HTTP request uses methods other than GET or POST, or includes custom headers (like Authorization or Content-Type: application/json), the browser sends an automatic preflight OPTIONS request before the actual payload is transmitted.
CORS is enforced strictly by web browsers to protect end-users from malicious cross-site scripting (XSS) and unauthorized cross-domain data reading. Backend servers, CLI tools, and desktop API clients (like cURL and Postman) bypass browser security policies and ignore CORS headers.
Free, browser-based utilities to test, generate, and inspect Cross-Origin Resource Sharing (CORS) payloads directly.
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