Free API CORS tester

Paste a JSON API URL and this page calls it from your browser, exactly as your own front-end code would. If the call succeeds, the API sends CORS headers that allow browser use. If it fails with a network error, the API most likely blocks cross-origin requests and you need a proxy or a different API. Nothing is sent to our servers: the request goes straight from your browser to the URL you enter.

How to read the result

• Works: the browser allowed the response, so fetch() from a static page will work too. The tool shows the status, content type and the top-level JSON keys.
• Blocked or failed: a browser gives the same error for a missing CORS header, a dead host and a mixed-content block (an http:// API called from an https:// page), so check those three in that order. It cannot tell them apart, and neither can your own code.
• Some APIs only fail here: a few reject requests from unknown origins or rate-limit shared browsers. A pass is reliable, a fail is a prompt to investigate.

Looking for APIs that already passed? The free CORS-enabled API list and the free weather API list were probed on 7 Oct 2026. The paid Keyless API Atlas covers 161 of them with curl and fetch snippets.