What is this?
Less is a dynamic stylesheet language that extends CSS with variables, mixins, nesting and functions, and Less.js is its official compiler written in JavaScript; this repo is the Less.js monorepo.
Less is a dynamic stylesheet language that extends CSS with variables, mixins, nesting and functions, and Less.js is its official compiler written in JavaScript; this repo is the Less.js monorepo.So I write .less files and get CSS back — how does it ship?Everything lives in one project: you write .less files, and Less.js compiles them into plain CSS. It ships as an npm package you can drive from the command line or call as a JavaScript library, with the compiler itself in the packages/less package of this monorepo.
Everything lives in one project: you write .less files, and Less.js compiles them into plain CSS. It ships as an npm package you can drive from the command line or call as a JavaScript library, with the compiler itself in the packages/less package of this monorepo.How do I get it compiling my styles?Install the compiler with npm (npm install -g less) and run lessc styles.less styles.css; you can also drop less.js into a page and let it compile styles in the browser. Usage and configuration options are documented at lesscss.org.
Install the compiler with npm (npm install -g less) and run lessc styles.less styles.css; you can also drop less.js into a page and let it compile styles in the browser. Usage and configuration options are documented at lesscss.org.What do I need on my machine before it will run?Just Node.js and npm — Less.js is written in JavaScript, with no Python, native builds or other runtimes required. The in-browser flavor needs nothing but a script tag.
Just Node.js and npm — Less.js is written in JavaScript, with no Python, native builds or other runtimes required. The in-browser flavor needs nothing but a script tag.Should I compile styles in the browser or in a build step?Browser-side compilation is a real mode, but every page load then ships the compiler and transforms styles at runtime, so production projects precompile .less to .css during the build instead. Note also that the repo readme is contributor-facing; day-to-day usage lives at lesscss.org.
Browser-side compilation is a real mode, but every page load then ships the compiler and transforms styles at runtime, so production projects precompile .less to .css during the build instead. Note also that the repo readme is contributor-facing; day-to-day usage lives at lesscss.org.Why would a web developer pick Less over plain CSS today?For authoring superpowers with standard CSS as the output: variables, mixins, nesting and functions on top of syntax you already know, and since Less is backwards-compatible with CSS your existing stylesheets work as-is.
For authoring superpowers with standard CSS as the output: variables, mixins, nesting and functions on top of syntax you already know, and since Less is backwards-compatible with CSS your existing stylesheets work as-is.Does the compiler run on Windows and macOS, or is it a Linux-only thing?It is a plain npm package, so it runs wherever Node.js runs — Windows, macOS and Linux alike — and the browser mode works in any modern browser regardless of OS.
It is a plain npm package, so it runs wherever Node.js runs — Windows, macOS and Linux alike — and the browser mode works in any modern browser regardless of OS.Am I allowed to use it in commercial projects?Yes — Less.js is distributed under the Apache License (Apache-2.0), which permits commercial and closed-source use as long as the license notice is kept.
Yes — Less.js is distributed under the Apache License (Apache-2.0), which permits commercial and closed-source use as long as the license notice is kept.What does Less add on top of CSS?Variables, mixins (reusable blocks of declarations), nested rules, operators and built-in functions for color and math — all compiled away by Less.js, so browsers only ever see standard CSS.
Variables, mixins (reusable blocks of declarations), nested rules, operators and built-in functions for color and math — all compiled away by Less.js, so browsers only ever see standard CSS.How does Less compare to Sass?Both are mature CSS preprocessors. Less stays closest to plain CSS syntax and is written in JavaScript, which is why it can run both in Node builds and directly in the browser; Sass brings its own feature set and tooling.
Both are mature CSS preprocessors. Less stays closest to plain CSS syntax and is written in JavaScript, which is why it can run both in Node builds and directly in the browser; Sass brings its own feature set and tooling.What is inside this monorepo?The main compiler package in packages/less with its own test suite (npm test), ESLint linting and scripts for publishing releases. The language documentation lives separately at lesscss.org.
The main compiler package in packages/less with its own test suite (npm test), ESLint linting and scripts for publishing releases. The language documentation lives separately at lesscss.org.Is Less still actively maintained?Yes — it has been developed since February 2010, holds around 17,000 stars, and the repo shows current activity: copyright notices through 2025, GitHub Actions workflows for CI and publishing, and a maintained changelog.
Yes — it has been developed since February 2010, holds around 17,000 stars, and the repo shows current activity: copyright notices through 2025, GitHub Actions workflows for CI and publishing, and a maintained changelog.What are similar projects?babel, gopherjs, postcss, TypeScript, closure-compiler, oxc, snowpack, sass
babel, gopherjs, postcss, TypeScript, closure-compiler, oxc, snowpack, sassWhich topics is it in?build-tools, less, dsl, styling, transpiler, language, compiler, css, browser, web-development, npm, frontend
build-tools, less, dsl, styling, transpiler, language, compiler, css, browser, web-development, npm, frontend