Zopfli

Zopfli is a compression library and command-line tool that produces exceptionally small DEFLATE, zlib, and gzip streams by spending more CPU time to search for better encodings. It keeps strict compatibility with the ubiquitous DEFLATE format, so outputs can be decompressed by any standard tool or browser. The encoder performs exhaustive block splitting and greedy but thorough match searching to shave extra bytes off assets, which is ideal for web content and firmware where size matters more than compression time. A companion utility, zopflipng, targets PNGs by trying alternate filter strategies and recompressing IDAT chunks, often achieving additional savings without changing image quality. The codebase includes both a reusable library and ready-to-use CLI tools for bulk optimization in build pipelines. It is frequently used offline—e.g., as a final step in release builds—because decode speed remains normal while files get smaller.