$ curl --http2 --http3

Which HTTP versions does a site support? The server makes real HTTP/1.1 and HTTP/2 requests, follows redirects (up to 8), and reports a timing breakdown, HSTS, compression and whether HTTP/3 is advertised. Only public hosts on ports 80, 443, 8080, 8443.

HTTP/3 runs over UDP/QUIC, which this host cannot send, so HTTP/3 is reported from the site's Alt-Svc header: that shows what the server advertises to browsers, not a completed HTTP/3 request. Timings are measured from the Phoenix server.