Brotli compression
Also called: brotli, br compression, brotli algorithm
Brotli is a lossless compression algorithm developed by Google that shrinks text-based web files (HTML, CSS, JavaScript) before they travel from server to browser. It usually produces smaller files than gzip, so pages transfer faster. Servers signal it with the Content-Encoding: br header.
Brotli combines an LZ77 variant, Huffman coding, and second-order context modeling, and it ships with a built-in dictionary of common web strings. Its sliding window reaches about 16 MiB, versus gzip’s 32 KiB, so it finds more repeated patterns and packs text tighter.
The practical win is transfer size. On the same file, Brotli usually beats gzip by a few percentage points, and at its most aggressive setting it can cut 15 to 25 percent more than gzip. Google’s own guidance is direct: prefer Brotli over gzip wherever possible.
Quality levels matter
Brotli exposes quality levels 0 to 11. Level 11 gives the smallest file but compresses slowly, so it fits static assets that are compressed once and cached. For dynamic responses built per request, a middle level (many servers default to 5 or 6) balances file size against CPU time. Compressing already-compressed formats like JPEG, PNG, or WOFF2 fonts wastes CPU for near-zero gain, so target HTML, CSS, JS, SVG, and JSON.
Negotiation is automatic. The browser advertises Accept-Encoding: gzip, br, and the server replies with Content-Encoding: br when both sides agree, falling back to gzip for older clients that do not support it.
How it affects your traffic
Smaller transfer sizes shorten load time, which feeds Core Web Vitals (Largest Contentful Paint especially) and the mobile page experience Google measures. Faster pages also give crawlers cheaper fetches and hold impatient users. Missing or misconfigured Brotli is a quiet, common drag we catch in a Technical SEO audit, along with checking you are not double-compressing assets or serving br on only some routes.
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