CORS Checker
Enter a URL to check CORS configuration — see allowed origins, methods, headers, and credentials policy. Diagnose CORS errors instantly. Free, no sign-up.
What is CORS?
Cross-Origin Resource Sharing (CORS) is a browser security mechanism that controls which origins can access resources on a server. It uses HTTP headers like Access-Control-Allow-Origin to determine if a cross-origin request should be allowed.
How does CORS work?
When a browser makes a cross-origin request, it sends an OPTIONS preflight request first (for non-simple requests). The server responds with CORS headers indicating which origins, methods, and headers are allowed. If the response does not include the right headers, the browser blocks the response.
Common CORS errors
The most common CORS error is No 'Access-Control-Allow-Origin' header — meaning the server did not permit the requesting origin. Other issues include missing credentials support, blocked headers, or wildcard origins incorrectly combined with credentials.
Why use CORS Checker online?
CORS Checker in the browser saves context switching: no DevTools needed, no server-side scripts, and instant diagnosis. It is ideal for debugging API integrations, testing cross-origin requests, and resolving CORS configuration issues.
Tips for best results
Test against your actual API endpoint, not just the base domain. Check both simple and preflight requests. Use this alongside browser DevTools Network tab for full diagnosis.
How to use
- Enter the target API URL you want to check.
- Click Check CORS to send a test request.
- Review connectivity status and CORS headers.
- Check security notes for potential issues.
- Use the findings to configure your server's CORS policy.
- Need another utility? Scroll to Related Tools below for CORS Checker companions on skybin.io.
Online tool vs terminal
| Terminal / CLI | This tool |
|---|---|
| Use curl -v to inspect response headers | Enter any URL and get instant CORS analysis |
| Check DevTools Network tab for preflight requests | See pass/fail status with color-coded headers |
| Guess CORS configuration from raw headers | Get security notes for common CORS issues |
CORS checks happen entirely in your browser. No URLs or results are sent to any server.
Frequently Asked Questions
- What is CORS?
- CORS (Cross-Origin Resource Sharing) is a browser security mechanism that uses HTTP headers to tell browsers whether a web application running at one origin can access resources from another origin.
- How do I fix CORS errors?
- Configure your server to send the appropriate CORS headers: Access-Control-Allow-Origin (set to your frontend origin or *), Access-Control-Allow-Methods, and Access-Control-Allow-Headers for preflight requests.
- What does a wildcard origin mean?
- Access-Control-Allow-Origin: * allows any origin to access the resource. This is convenient for public APIs but cannot be used with credentials (cookies, Authorization headers). For authenticated requests, specify exact origins.
- Is this tool free to use?
- Yes. All Skybin developer tools are free with no account, API key, or usage limits.
- Does my data get sent to a server?
- No. CORS checks happen entirely in your browser. The target URL is accessed directly by your browser, not relayed through Skybin's servers.
- Can I use this on mobile?
- Yes. The tool works in modern mobile browsers, though a desktop screen is easier for reviewing CORS headers.
- Why can't I see CORS headers for some sites?
- Some sites block cross-origin requests entirely, or the browser's CORS policy prevents reading headers without explicit server permission. Try testing from a server-side context in those cases.
- Are there keyboard shortcuts?
- Press Enter in the URL input to trigger a check. Copy buttons provide one-click output.
- Does Skybin store my checks?
- No. We do not log URLs or results. Refreshing the page clears in-memory state.