Zopfli

Zopfli is a data compression library that writes deflate, gzip and zlib streams and reaches higher compression ratios than mainstream Deflate and zlib implementations, at the cost of running more slowly. It iterates entropy modeling together with a shortest path search to find a low bit cost path through the graph of all possible Deflate representations of the input. By default it performs 15 iterations, and its output is typically 3 to 8 percent smaller than zlib's maximum compression while taking around 80 times longer, so it suits one-time compression of static content such as web assets, PNG images, WOFF fonts and zip-based package files rather than on-the-fly compression. It is based on an algorithm of Jyrki Alakuijala, the first reference implementation by Alakuijala and Lode Vandevenne appeared from Google in February 2013 under the Apache License 2.0, and Google archived the project in October 2025.