CleanCSS

CleanCSS, commonly written as clean-css, is an open-source CSS minifier and optimizer for Node.js. It provides a library API and a command-line interface that streamlines reducing CSS file size. The tool minimizes CSS by removing comments and unnecessary whitespace, while applying optimizations such as merging identical selectors, shortening zero values, optimizing shorthand properties, and rewriting color values. It can also rebase URL references when configured and generate source maps to aid debugging.

CleanCSS is designed to be fast and suitable for integration into build pipelines. It is used in server-side scripts and front-end workflows to produce compact CSS assets. It can be invoked from the command line or embedded in JavaScript projects via the library. It integrates with common task runners and bundlers such as Grunt, Gulp, Webpack, and npm scripts, enabling automated CSS minification as part of a wider pipeline.

Options provided by CleanCSS cover its level of optimization and compatibility. Users can control whether to keep line breaks, enable source maps, handle legacy browser compatibility, override URL rebasing behavior, and tune aggressive merging of rules and properties. The tool aims to preserve the visual output while reducing file size, but as with all minifiers, edge cases may require manual verification.

CleanCSS is released under an open-source license (MIT) and is maintained on its GitHub repository with contributions from the community. It remains a commonly used component in web performance optimization workflows.