What does the CORS Validator check?

It audits pasted HTTP response headers and checks whether Access-Control settings are likely to allow or block a browser request safely.

What does the optional Origin and Target URL check add?

It checks same-origin status, origin allowlist membership, and HTTPS use for the calling origin. It analyzes the values you provide and does not request either URL.

Does the validator fix a CORS problem?

No. It reports errors, warnings, and recommendations, but the server or API owner must change the response headers. A wildcard origin combined with credentials is a common configuration error.

No. The headers and URLs are parsed entirely in your browser and are never sent anywhere.

CORS Header Validator

Validate Cross-Origin Resource Sharing (CORS) headers for security and compliance

Request Configuration

Origin URL (Optional)

The URL making the cross-origin request

Target URL (Optional)

The API/resource URL being requested

CORS Response Headers

Enter response headers from the server (one per line, in "Name: Value" format)

CORS Headers Reference

Response Headers:

Access-Control-Allow-Origin - Allowed origins
Access-Control-Allow-Methods - Allowed HTTP methods
Access-Control-Allow-Headers - Allowed request headers
Access-Control-Allow-Credentials - Allow cookies/auth
Access-Control-Max-Age - Preflight cache duration
Access-Control-Expose-Headers - Exposed response headers

Best Practices:

• Avoid wildcard (*) in production
• Use specific origins when possible
• Be cautious with credentials
• Limit allowed methods and headers
• Use HTTPS for secure applications
• Set appropriate cache duration

Learn More:

For detailed CORS documentation, visit theMDN CORS Guide

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