less

Less.js

The dynamic stylesheet language. lesscss.org

[!IMPORTANT] This package README is for Less 5 alpha.1. Less 5 is a Jess-powered compiler preview for early testing and is not yet a drop-in replacement for Less 4.x. It covers Node.js less.render(), less.renderFile(), and lessc, plus variables, arithmetic, mixins, imports, and nested-rule output. Source maps, URL rewriting, and compress now work through the less.render() API; the legacy @plugin hook ABI is intentionally not carried over (function plugins are supported). See the Less 5 feature status for the full list of what is implemented, in progress, and intentionally not.

Less extends CSS with variables, mixins, functions, nesting, and more — then compiles to standard CSS. Write cleaner stylesheets with less code.

@primary: #4a90d9;

.button {
  color: @primary;
  &:hover {
    color: darken(@primary, 10%);
  }
}

Install

npm install less@alpha

For a pinned first alpha:

npm install less@5.0.0-alpha.1

Usage

Node.js

Less 5 alpha.1 requires Node.js ^20.19.0 || >=22.12.0.

import less from 'less';

const output = await less.render('.class { width: (1 + 1) }');
console.log(output.css);

Command Line

npx lessc styles.less styles.css

Browser

A browser build ships in the package (dist/less-browser-dev.js) and defines window.less with the same render API; it powers the online playground. Full browser-API parity with Less 4 is still being validated — see the feature status.

Why Less?

• Variables — define reusable values once
• Mixins — reuse groups of declarations across rulesets
• Nesting — mirror HTML structure in your stylesheets
• Functions — transform colors, manipulate strings, do math
• Imports — split stylesheets into manageable pieces
• Extend — reduce output size by combining selectors

Documentation

Full documentation, usage guides, and configuration options at lesscss.org.

Contributing

Less.js is open source. Report bugs, submit pull requests, or help improve the documentation.

See CONTRIBUTING.md for development setup.

License

Copyright (c) 2009-2025 Alexis Sellier & The Core Less Team Licensed under the Apache License.

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