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CORS Header Validator

CORS Header Validator

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

Request Configuration

The URL making the cross-origin request

The API/resource URL being requested

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

    About this tool

    Validate Cross-Origin Resource Sharing headers for security compliance CORS Header Validator runs in the browser on DevTools. There is no signup, and your input stays on this device unless the tool explicitly performs a live network lookup.

    What this tool does not do

    • CORS Header Validator is a free in-browser utility, not a hosted API. It does not keep server-side history and is not a substitute for production verification in your own stack.

    How do I use this tool?

    1. How do I use CORS Header Validator?

      Open CORS Header Validator, enter or paste your input, and copy the result. The page works without an account.

    Related guides

    CORS Explained: A Practical Guide for Web Developers

    Understand Cross-Origin Resource Sharing from the browser up. Learn why CORS is a browser mechanism, the difference between simple and preflight requests, the wildcard-with-credentials pitfall, and how to read Access-Control-* headers.

    HTTP Status Codes Every Developer Should Know

    A field guide to HTTP status codes — what each 1xx–5xx class means, the codes you will meet every day, and the common mistakes people make reading them.

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