CORS Checker

Analyze CORS headers for misconfigurations.

CORS response headers

What Is a CORS Checker?

The CORS Checker analyzes Cross-Origin Resource Sharing headers to detect misconfigurations. It reviews Access-Control-Allow-Origin, Allow-Credentials, Allow-Methods, and Vary, and warns about risky patterns such as wildcard origins combined with credentials or missing Vary: Origin. This free online security tool is useful for CORS checker, CORS configuration checker, Cross-Origin Resource Sharing tester. Common use cases include reviewing allowed origins, credentials, methods, and cache-related CORS configuration. It is designed for quick browser-based analysis and development workflows. Security checks are signals rather than guarantees, so production systems should also be validated against current standards and their specific threat model.

How to Use This CORS Checker

1
Provide the configurationPaste the relevant policy or response headers into the analyzer.
2
Run the analysisLet the tool inspect the supplied directives and values.
3
Review warningsIdentify settings that are missing, overly broad, unsafe, or inconsistent.
4
Compare with application needsA secure configuration must still allow the resources and cross-origin behavior your application requires.
5
Retest after changesUpdate the server configuration and run the analyzer again.

Frequently Asked Questions

CORS is a browser mechanism that controls whether a web page at one origin may request resources from another origin. It is configured with HTTP response headers.

Combining Access-Control-Allow-Origin: * with Access-Control-Allow-Credentials: true is invalid in browsers. Using '*' with cognizance makes resources readable cross-origin.

When responses vary by origin, the Vary: Origin header prevents caches from serving a response for one origin to another, which could leak data.

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