Use this little website to test if a URL is setup correctly to work with CORS.
Shareable link: https://cors-test.codehappy.dev/?method=get&origin=https%3A%2F%2Fcors-test.codehappy.dev%2F&url=https%3A%2F%2Fivancarlos.com.br%2F.well-known%2Fnostr.json
These are the response headers received when making the request.
access-control-allow-origin: *
alt-svc: h3=":443"; ma=86400
cf-cache-status: DYNAMIC
cf-ray: a0872a3c1978e88e-CMH
connection: close
content-type: text/html, application/json
date: Mon, 08 Jun 2026 10:20:37 GMT
server: cloudflare
strict-transport-security: max-age=31536000; includeSubDomains; preload
transfer-encoding: chunked
vary: Accept-Encoding
CORS tester was built by @mscccc. The code is available on GitHub. Sponsored by HTML/CSS to Image.