Beyond Static Resources: Delta Compression for Dynamic HTML

Compression Dictionary Transport ( RFC 9842 ), authored by Patrick Meenan and Yoav Weiss, lets browsers use previously seen content as compression dictionaries, dramatically reducing transfer sizes. The standard is shipped in Chromium-based browsers (Chrome, Edge, Opera…etc.), with Firefox actively working toward enabling it. Early production deployments have shown double-digit percentage reductions in HTML payload sizes and measurable improvements to Largest Contentful Paint . And there's a natural next step—one that could extend these benefits to the majority of the web's traffic. (Note: While the standard supports multiple algorithms including Zstandard, this article will use Brotli and its dcb encoding for the purposes of demonstration). Where Compression Dictionaries shine today Compression Dictionary Transport was designed around two powerful use cases: Use case 1: Delta compression for versioned static resources. Your browser has app.v1.js cached. You deploy app.v2.js . The brow