Brotli Compression

In 2015, Google released Brotli, a compression algorithm designed specifically for web content. Their key insight: web pages are not random text. They are built from a predictable vocabulary of HTML tags, CSS properties, JavaScript keywords, and URL patterns. Brotli ships with a pre-built dictionary of 120KB of these common web patterns. When compressing a <div class="container">, gzip has to learn that pattern from scratch. Brotli already knows it.

The result: 15-25% better compression than gzip on typical web content, with comparable decompression speed. Cloudflare rolled out Brotli in 2017 and measured a 17% average reduction in response sizes compared to gzip across their entire network. For a CDN serving petabytes of traffic daily, that 17% translates to massive bandwidth savings.

Every major CDN (Cloudflare, CloudFront, Fastly, Vercel, Netlify) now serves Brotli by default. If your static assets are still gzip-only, switching to Brotli is free performance.

Both gzip and Brotli compress text by finding repeated patterns and replacing them with short references. The difference is in their dictionaries and algorithms:

Gzip (DEFLATE algorithm, 1996):

• Builds its dictionary from the data being compressed
• Sliding window of 32KB (looks at the last 32KB to find matches)
• Fast compression, fast decompression
• No built-in knowledge of web content

Brotli (2015):

• Ships with a 120KB static dictionary of common web patterns
• Sliding window up to 16MB (finds matches across much larger spans)
• Slower compression at high levels, fast decompression
• 11 compression levels (vs gzip's 9)

The static dictionary is Brotli's superpower. Common strings like <html, </div>, function, return, https://, text/html, application/json are already in the dictionary. Brotli encodes them as short references without needing to discover them in the data first. This is why Brotli wins biggest on HTML, CSS, and JavaScript, those formats are built entirely from dictionary-friendly patterns.

For non-web content (database dumps, log files, binary data), the dictionary advantage disappears and Brotli's improvement over gzip shrinks to 5-10%.