postCSS

PostCSS is an open-source tool for transforming CSS using JavaScript plugins. It runs on Node.js and provides a plugin-based API that allows developers to analyze, modify, or extend CSS. Unlike traditional preprocessors such as Sass or Less, PostCSS does not introduce a separate syntax; instead, it processes CSS through plugins that operate on an abstract syntax tree (AST).

The core idea is a small runtime plus a large ecosystem of plugins. PostCSS parses CSS into an AST, runs a sequence of plugins that can modify, add, or remove rules and declarations, and then stringifies the AST back to CSS. Plugins can perform tasks such as autoprefixing, minification, custom properties, nesting, imports, and linting. Notable plugins in the ecosystem include Autoprefixer, cssnano, postcss-preset-env, postcss-import, and postcss-nested.

Usage and integration are common in modern web development. PostCSS is often invoked via the command line or through build tools, and it integrates with Webpack, Rollup, Parcel, Gulp, and other ecosystems through plugins like postcss-loader or configuration files such as postcss.config.js. A typical setup specifies which plugins to run and in what order, enabling workflows that polyfill future CSS features and optimize output for production.

History and reception: PostCSS has grown into a widely adopted tool due to its modular, extensible architecture. Its plugin approach allows teams to tailor CSS tooling to their needs, balancing future CSS capabilities with current browser support, without imposing a single prescriptive workflow.