A new implementation of dictionary compression using Zstandard and Brotli is achieving compression ratios that seemed impossible a few years ago. For developers shipping web apps, this could mean dramatically faster load times and lower bandwidth costs.
Let me explain what dictionary compression is and why it matters. Normal compression works on individual files—find patterns, encode them efficiently, done. Dictionary compression trains on multiple similar files to build a shared dictionary of common patterns. When you compress a new file using that dictionary, you get much better ratios.
The problem has always been that dictionary compression requires both the compressor and decompressor to have the same dictionary. That's easy in controlled environments but hard on the web where you can't assume clients have your custom dictionary.
What changed? Browsers now support shared dictionaries. Chrome and Firefox can fetch a compression dictionary once and reuse it for multiple resources. This makes dictionary compression practical for web delivery.
The benchmarks from HTTP Toolkit are impressive. They're seeing compression improvements of 70-90% on JavaScript bundles compared to standard Brotli. That means if your app bundle is 1MB compressed, it could drop to 100-300KB with dictionary compression.
For web performance engineers, this is huge. A 70% reduction in transfer size means faster load times, especially on slow connections. It means lower bandwidth costs for high-traffic sites. It means better user experience on mobile devices with expensive data plans.
What I like about this is that it's actual technical innovation, not hype. Dictionary compression has existed for decades. What's new is browser support making it practical. The technology works. The standards exist. The tooling is available.
The question is adoption. Will CDNs and hosting providers support this? Will frameworks like React and Next.js integrate it? Will companies invest in building good dictionaries for their codebases? Or will this remain a niche optimization that only performance nerds care about?
The technology is impressive. The question is whether the web development community will actually use it. I hope so, because 70% smaller bundles would make the web a lot faster.
