CSSO – CSS Optimizer

CSSO (CSS Optimizer) is a CSS minifier that performs cleaning (removing redundancies), compression (replacing with shorter forms), and restructuring (merging declarations/rules) to reduce CSS file size. Version 5.0.5 (latest stable) supports ESM and CommonJS dual module, CSS Selectors Level 4, and ships TypeScript definitions. It is built on CSSTree for AST parsing and manipulation. Compared to other minifiers like clean-css, CSSO offers structural optimizations beyond simple compression. Maintained actively with frequent releases.