This package contains functions for compressing and decompressing data streams and is based on the well-known zlib library. In this implementation, error handling is performed not through raising exceptional states, but through returning error codes from functions, which makes the application somewhat "lighter". Authors of adaptation: Alexey Shuvalov, later update to version zlib 1.1.4 was performed by Dimaxx.

The KOLZlib module has been used successfully, at least in the KOLPng package (see the section on KOL graphical extensions).