HTTP/3 Test

HTTP/3 is the newest version of the protocol browsers use to load websites. It runs over QUIC, which uses UDP instead of TCP, and it recovers faster from lost packets and slow networks than HTTP/2. Browsers fall back to HTTP/2 when it isn't available.

Enter its host name above. If we see HTTP/3 advertised and a QUIC server answering on UDP 443, the result says HTTP/3 is on. In a browser you can also open the developer tools, look at the Network tab and show the protocol column, where h3 means HTTP/3.

We check from our server in Germany only. A firewall that blocks our server, a CDN that answers some regions differently, or UDP 443 closed to outside traffic can all make HTTP/3 look off from here while it works for your visitors. The check isn't a full HTTP/3 request either.

QUIC is the transport protocol underneath HTTP/3. It was first built by Google and became a standard in 2021 (RFC 9000). It builds encryption into the connection and uses UDP port 443.

You don't need it, and HTTP/2 works everywhere. HTTP/3 helps most on mobile and unreliable connections. It's worth turning on if your server or CDN offers it as a switch, since browsers fall back to HTTP/2 on their own.

It's a DNS record that tells browsers which protocols a site supports before they connect. An alpn value of h3 lets a browser use HTTP/3 on its first visit, without waiting to see an Alt-Svc header. Not every site has one.

Each visitor can run 2 checks a minute and 10 an hour, and each host can be checked 20 times an hour. When a check finishes without an error we keep it for 5 minutes, and repeat views of it don't count. Checks that ended in an error are not kept.

We keep a finished check for 5 minutes so repeat views are instant, and our server logs which host was checked for 14 days so we can deal with abuse. We don't store your IP address, only a scrambled form of it.