How to Use CORS Debugger
Enter your frontend URL and API URL and this tool explains whether CORS applies, whether the browser will send a preflight, and the exact Access-Control-* response headers your API must return — including the common credentials-plus-wildcard mistake. A rules-based explainer (it can't send the request, since the browser would block it).
Open the CORS Debugger tool →What is CORS Debugger?
Explain a CORS problem: enter your frontend and API URLs to see exactly which headers the server needs. It's completely free, needs no sign-up, and runs entirely in your browser — so it's fast and private.
How to use CORS Debugger
- Open the CORS Debugger tool.
- Paste or type your input.
- Set any options provided.
- Copy the result. Everything runs in your browser — nothing is uploaded.
Frequently asked questions
Can it actually send the request?
No — if there were a CORS problem the browser would block it anyway. Instead it explains, from the rules, exactly which response headers your API needs.
What's the most common CORS mistake?
Using Access-Control-Allow-Origin: * together with credentials. With cookies/credentials the header must echo the exact origin and include Access-Control-Allow-Credentials: true.
Ready to try it?
Open CORS Debugger →