Compression test
Confirm your server compresses responses with gzip or Brotli.
This gzip test inspects the response headers to confirm whether your server compresses content with gzip or the more efficient Brotli algorithm. It reports the encoding in use and the size savings, since compressed text assets can shrink dramatically and load faster over the wire. A result showing no compression means visitors are downloading larger payloads than necessary, hurting speed and bandwidth. Compression settings can be reset by a server or CDN change, so it's worth re-testing after changes.
Frequently asked questions
Should I use gzip or Brotli?
Brotli generally produces smaller files for text-based assets and is widely supported by modern browsers, while gzip remains a reliable fallback. Serving Brotli with gzip as a fallback is a common best practice.
Which files benefit most from compression?
Text-based resources like HTML, CSS, JavaScript, JSON, and SVG compress well, whereas already-compressed formats like JPEG and PNG see little benefit.
Why does the saving estimate vary?
Compression ratio depends on the content — highly repetitive text compresses far more than dense or already-minified assets, so the percentage differs per page.
How does the server know to compress?
The browser advertises support with an Accept-Encoding request header (gzip, br), and the server responds with a Content-Encoding header naming what it used. If the response lacks Content-Encoding, no compression was applied.
Why might my server not be compressing?
Compression may be disabled in the server or CDN config, restricted to certain MIME types, or skipped for responses below a minimum size threshold. Check that text content types are enabled and the threshold isn't too high.
Can compression be a security risk?
Compressing secret data alongside attacker-influenced input enabled old attacks like BREACH. In practice, compressing static assets is safe; just avoid compressing responses that mix sensitive tokens with reflected user input.
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