HTTP/2 and HTTP/3

HTTP/2 and HTTP/3 are versions of the HTTP protocol that change how browsers fetch multiple assets. HTTP/2 uses one TCP connection with multiplexing; HTTP/3 uses QUIC over UDP to reduce handshake latency and head-of-line blocking.

The core differences

How to check

In DevTools → Network, enable the Protocol column. h2 means HTTP/2, h3 means HTTP/3. From a terminal, curl -I --http2 https://example.com checks HTTP/2 support. HTTP/3 usually needs a recent curl and a specific flag.

What to watch for

• HTTPS is required. Modern browsers only use HTTP/2 and HTTP/3 on secure connections.
• The server and CDN must support it. LiteSpeed, Nginx, and major CDNs generally do.
• It is not a cache replacement. The protocol speeds up transfer; large assets are still large.
• HTTP/3 is not always faster. On stable networks, the difference can be small.
• Asset priority still matters. Many streams do not remove the cost of heavy JavaScript and images.

The difference is barely noticeable on a page with one small file. Multiplexing helps when there are many assets, especially on high-latency connections. If the server does not support HTTP/2 yet, prioritize HTTPS and caching before changing protocols. A CDN is often the fastest way to enable HTTP/3, but test in staging first. Check the header on every asset type as well.

FAQ