What is HTTP compression?

A web server can compress a page, script or stylesheet before sending it, and the browser unpacks it on arrival. The browser lists the formats it understands in its Accept-Encoding request header, and the server names the one it used in Content-Encoding. Text compresses well, so a compressed page often travels at a quarter of its size or less, which makes it load faster and saves bandwidth.

Encoding Header value Notes
gzip gzip Supported everywhere; the baseline every server should have
Brotli br Usually 15–25% smaller than gzip for text; HTTPS only
Zstandard (zstd) zstd Newer; fast to compress, supported by Chrome and Firefox

Tool description

Enter a URL and press Check compression. Our server downloads it once uncompressed and once for each encoding, then compares the sizes:

  • Supported says whether the server answered with that encoding
  • Size is how many bytes were sent compressed, and Saved how much smaller that is than the Uncompressed size
  • Vary: Accept-Encoding says whether the server tells caches and CDNs that the answer depends on the encoding, so they don't hand a compressed copy to a client that can't read it

Redirects are followed (up to 5), and the Checked URL shows where they ended. Each download is read up to 5 MB.

AI assistants connected to the Rapid Tool Set MCP server can run the same check as http_compression_checker.

Tips

  • Check the files that matter most for speed: the page itself, its main JavaScript bundle and its CSS.
  • Images, videos and fonts such as WOFF2 are compressed already; servers rightly send them without HTTP compression.
  • If Brotli is missing, it's often a single setting: brotli on; with the ngx_brotli module in nginx, or mod_brotli in Apache. CDNs such as Cloudflare enable it for you.