How can I check which HTTP version a site is using?
Use curl with the --http2 or --http3 flags and read the response line, or open browser developer tools, add the Protocol column to the network panel and read h2 or h3. Servers advertise HTTP/3 through the Alt-Svc header, so first visits often still use HTTP/2.
Answered in
HTTP/1.1, HTTP/2 and HTTP/3: What Each Version Fixed and What It Left BrokenPersistent connections, multiplexing, header compression and QUIC: each HTTP version removed one bottleneck and exposed the next. How to choose and verify.
Read the full analysisOther questions this article answers
More web performance questions
- What problem does HTTP/2 solve compared with HTTP/1.1?
- What is head-of-line blocking and does HTTP/2 remove it?
- Why does HTTP/3 use UDP?
- What is the difference between latency, bandwidth and throughput?
- Why measure p95 and p99 instead of the average?
- What is the quickest win for network latency?
- How do I decide whether to make something asynchronous?
- What is a cold start?
Every answer on Crashtech is written by the editor of the article it comes from — never auto-summarised. Browse all answers or the Web Performance beat.