corscheck
Check a URL's CORS headers and whether browsers allow it
About corscheck
corscheck is a free web tool for developers who need to know whether a cross-origin browser request to an API or URL would be allowed. Paste a URL, optionally add the origin you want to test, and it shows the CORS headers the server actually returns, along with an allowed or blocked verdict.
The tool simulates a preflight request when one is needed and flags concrete misconfigurations, so you can see what is wrong rather than guessing from console errors. No signup is required for the free checks.
A paid report at 0.02 USDC on Base checks several origins at once, probes for a reflect-any-origin security weakness, and provides ready-to-paste fix snippets for Express, Nginx, FastAPI and Cloudflare Workers. It is built by Doormat Capital and submitted to Twelve Tools.
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