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Inspect & debugHTTP/2 & Compression

HTTP/2, HTTP/3 & Compression Checker

HTTP/2, HTTP/3, compression and caching.

Redirects are followed. The final URL is then fetched once per encoding (gzip, br, zstd) to compare sizes; downloads stop at 5 MB. Timings are measured from our server, not your browser.

About the HTTP/2, HTTP/3 & Compression Checker

This tool shows how a server delivers a page. It opens a TLS connection offering h2 and http/1.1 and reports which protocol the server picks (ALPN), so you know whether HTTP/2 works. It reads the Alt-Svc header to see whether HTTP/3 is advertised; it doesn't connect over QUIC, so this confirms the advertisement only.

It then requests the final URL once uncompressed and once each with Accept-Encoding: gzip, br (Brotli) and zstd, and compares the sizes, so you can see which encodings the server will serve and how much each saves. Downloads stop at 5 MB. It checks that compressed responses send Vary: Accept-Encoding, measures DNS, connect, TLS and time to first byte from our server, explains Cache-Control and the other caching headers in plain English, and lists headers that reveal a CDN such as Cloudflare, CloudFront or Fastly.

How to use it

  1. Enter a URL or domain.
  2. Select Check.
  3. Read the summary cards, then the compression table and caching details.

Examples

Common questions

Why do my timings differ from the browser's?

They're measured from our server, so the distance to your server differs, and a browser may already have a connection open.

Is Brotli better than gzip?

For text it usually produces smaller files. Serve both: browsers that support Brotli ask for it, others get gzip.

Why isn't my image compressed?

JPEG, PNG, WebP and video are already compressed, so gzip or Brotli would gain almost nothing.