Glossary / HTTP/2

What is HTTP/2

HTTP/2 is the second major version of HTTP, the protocol the browser uses to talk to the server. Its main advantage over the older HTTP/1.1 is the ability to transfer many files at once over a single connection. As a result, pages with dozens of images and scripts load noticeably faster.

With HTTP/1.1 the browser fetched resources almost one by one and opened many separate connections, which caused bottlenecks. HTTP/2 introduces multiplexing: all requests run in parallel over one connection, with no queue. It also compresses HTTP headers and lets the server push needed files ahead of time.

HTTP/2 works almost only over HTTPS, so it needs an SSL certificate. Every modern browser and most hosts support it, and it is often on by default on LiteSpeed, Nginx, or through Cloudflare.

Moving to HTTP/2 usually speeds up loading with no changes to the site's code. The biggest gain is for sites with many small files.

Example

HTTP/2 200

Common mistakes

• Thinking HTTP/2 works without HTTPS, when in practice browsers only enable it over SSL.
• Believing you must rewrite the site, when the protocol turns on at the server level and the code stays untouched.
• Still bundling every script into one file, which no longer helps under HTTP/2 and can even hurt.
• Confusing HTTP/2 with HTTPS: one is about speed, the other about encryption.

Related terms

• TTFB What is TTFB (Time To First Byte)
• CDN What is a CDN (Content Delivery Network)
• HTTP/3 What is HTTP/3
• gzip / Brotli What is gzip and Brotli compression
• DNSBL What is a DNSBL (blacklist)