HTTP/2 & HTTP/3 Test
Which modern protocols does a site support?
HTTP/2 lets a browser fetch every asset over one connection instead of queuing them; HTTP/3 does the same over QUIC and recovers faster when packets are lost. This negotiates a real connection to find out what a site supports, and separately attempts an actual QUIC handshake rather than taking the Alt-Svc header's word for it.
Frequently asked questions
How much faster is HTTP/2?
It depends on how many resources a page loads. Under HTTP/1.1 a browser opens about six connections per host and queues everything else; with HTTP/2 they all share one connection. Pages with many small assets gain the most.
Do I need HTTP/3 as well?
It helps most on mobile and lossy networks, where a single lost packet under TCP stalls everything behind it. Get HTTP/2 working first — it is the bigger jump and far simpler to enable.
The site advertises h3 but the test could not confirm it. Why?
Alt-Svc is only an advertisement. QUIC runs over UDP and plenty of networks block or throttle it, so a server can advertise HTTP/3 that this connection could not actually establish.