Aless

ALess is a lightweight open-source CSS preprocessor and templating language designed to extend CSS with programmatic features while aiming for a small runtime and fast compilation. It compiles to standard CSS and is intended to fit into modern web development workflows, offering a concise alternative to larger preprocessors.

Key features of aLess include variables with lexical scope, nested selectors, and a system of mixins for reusable style fragments. It also provides parametric mixins, functions for color manipulation and math, and support for imports or partials to structure large style sheets. Optional control directives allow conditional logic and simple loops to generate CSS programmatically, enabling more dynamic styling without leaving the preprocessor environment. The syntax is designed to be approachable for developers familiar with CSS, while introducing enhancements common in other preprocessors.

The architecture typically centers on a JavaScript-based compiler that runs in Node.js. The compiler offers a command-line interface and can be used as a library within build systems. It supports source maps for easier debugging and is designed to integrate with popular tooling such as npm scripts, webpack, or task runners. Projects often organize code into modular files with aLess extension and rely on an import system to assemble final CSS.

History and development have been driven by a community of contributors focused on simplicity and performance. As with many CSS preprocessors, aLess aims to improve maintainability and reusability of styles while reducing repetition. The ecosystem is smaller than that of more established preprocessors, but it provides essential features for teams seeking a lightweight alternative.

See also: Less (CSS preprocessor), Sass, PostCSS.