Transport
HTTP/3 Checker
Check whether a site advertises HTTP/3 (QUIC) support via the Alt-Svc header, ALPN negotiation and DNS HTTPS records.
This checks the signals a server sends about HTTP/3 support — it doesn't attempt a live QUIC connection (QUIC runs over UDP, which isn't reachable this way from a standard server). A server can advertise support here without every client actually being able to negotiate it, and vice versa.
About this tool
Comprehensive documentation & audit utility guideHTTP/3 runs over QUIC (UDP) instead of TCP, cutting connection setup time and avoiding head-of-line blocking — a real speed win, especially on flaky mobile connections. There's no way to open a live QUIC connection from a standard server, so this checks the three signals a server actually sends about HTTP/3 support instead.
How it works
1
Enter a URL
Any public site you want to check.
2
We check three signals
Alt-Svc header, ALPN from a real TLS handshake, and the DNS HTTPS record.
3
See the verdict
Each signal shown individually, plus an overall likely-supported result.
What it checks
Alt-Svc response header advertising h3
ALPN protocol negotiated during a real TLS handshake
DNS HTTPS record's advertised ALPN list