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A tool set for CSS: fast detailed parser (CSS → AST), walker (AST traversal), generator (AST → CSS) and lexer (validation and matching) based on specs and browser implementations


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Package description

What is css-tree?

The css-tree npm package is a tool for parsing and manipulating CSS. It allows users to parse CSS strings into an abstract syntax tree (AST), walk over nodes in the tree, generate CSS strings, and more. It is useful for tasks such as CSS minification, linting, and transformation.

What are css-tree's main functionalities?

Parsing CSS to AST

This feature allows you to parse a CSS string and convert it into an abstract syntax tree (AST) for further manipulation or analysis.

const csstree = require('css-tree');
const ast = csstree.parse('.example { color: red; }');

Walking the AST

This feature enables you to traverse the AST and apply functions or extract information from specific nodes.

csstree.walk(ast, function(node) {
  if (node.type === 'ClassSelector') {

Generating CSS from AST

After manipulating the AST, you can generate a CSS string from the modified AST, which can be used in stylesheets or injected into web pages.

const modifiedAST = csstree.parse('.example { color: blue; }');
const css = csstree.generate(modifiedAST);

Minifying CSS

css-tree can be used to minify CSS by parsing it with compression options and then translating the AST back to a CSS string.

const compressedCSS = csstree.translate(csstree.parse('.example { color: red; }', { compress: true }));

Other packages similar to css-tree



2.3.1 (December 14, 2022)

  • Added :host, :host() and :host-context() pseudo class support (#216)
  • Fixed generator, parse and parse-selector entry points by adding missed NestedSelector node type
  • Removed npm > 7 version requirement (#218)



CSSTree logo


NPM version Build Status Coverage Status NPM Downloads Twitter

CSSTree is a tool set for CSS: fast detailed parser (CSS → AST), walker (AST traversal), generator (AST → CSS) and lexer (validation and matching) based on specs and browser implementations. The main goal is to be efficient and W3C spec compliant, with focus on CSS analyzing and source-to-source transforming tasks.


  • Detailed parsing with an adjustable level of detail

    By default CSSTree parses CSS as detailed as possible, i.e. each single logical part is representing with its own AST node (see AST format for all possible node types). The parsing detail level can be changed through parser options, for example, you can disable parsing of selectors or declaration values for component parts.

  • Tolerant to errors by design

    Parser behaves as spec says: "When errors occur in CSS, the parser attempts to recover gracefully, throwing away only the minimum amount of content before returning to parsing as normal". The only thing the parser departs from the specification is that it doesn't throw away bad content, but wraps it in a special node type (Raw) that allows processing it later.

  • Fast and efficient

    CSSTree is created with focus on performance and effective memory consumption. Therefore it's one of the fastest CSS parsers at the moment.

  • Syntax validation

    The build-in lexer can test CSS against syntaxes defined by W3C. CSSTree uses mdn/data as a basis for lexer's dictionaries and extends it with vendor specific and legacy syntaxes. Lexer can only check the declaration values currently, but this feature will be extended to other parts of the CSS in the future.

Projects using CSSTree

  • Svelte – Cybernetically enhanced web apps
  • SVGO – Node.js tool for optimizing SVG files
  • CSSO – CSS minifier with structural optimizations
  • NativeScript – NativeScript empowers you to access native APIs from JavaScript directly
  • react-native-svg – SVG library for React Native, React Native Web, and plain React web projects
  • penthouse – Critical Path CSS Generator
  • Bit – Bit is the platform for collaborating on components
  • and more...




Install with npm:

npm install css-tree

Basic usage:

import * as csstree from 'css-tree';

// parse CSS to AST
const ast = csstree.parse('.example { world: "!" }');

// traverse AST and modify it
csstree.walk(ast, (node) => {
    if (node.type === 'ClassSelector' && === 'example') { = 'hello';

// generate CSS from AST
// .hello{world:"!"}

Syntax matching:

// parse CSS to AST as a declaration value
const ast = csstree.parse('red 1px solid', { context: 'value' });

// match to syntax of `border` property
const matchResult = csstree.lexer.matchProperty('border', ast);

// check first value node is a <color>
console.log(matchResult.isType(ast.children.first, 'color'));
// true

// get a type list matched to a node
// [ { type: 'Property', name: 'border' },
//   { type: 'Type', name: 'color' },
//   { type: 'Type', name: 'named-color' },
//   { type: 'Keyword', name: 'red' } ]


Is it possible to import just a needed part of library like a parser or a walker. That's might useful for loading time or bundle size optimisations.

import * as tokenizer from 'css-tree/tokenizer';
import * as parser from 'css-tree/parser';
import * as walker from 'css-tree/walker';
import * as lexer from 'css-tree/lexer';
import * as definitionSyntax from 'css-tree/definition-syntax';
import * as data from 'css-tree/definition-syntax-data';
import * as dataPatch from 'css-tree/definition-syntax-data-patch';
import * as utils from 'css-tree/utils';

Using in a browser

Bundles are available for use in a browser:

  • dist/csstree.js – minified IIFE with csstree as global
<script src="node_modules/css-tree/dist/csstree.js"></script>
  csstree.parse('.example { color: green }');
  • dist/csstree.esm.js – minified ES module
<script type="module">
  import { parse } from 'node_modules/css-tree/dist/csstree.esm.js'
  parse('.example { color: green }');

One of CDN services like unpkg or jsDelivr can be used. By default (for short path) a ESM version is exposing. For IIFE version a full path to a bundle should be specified:

<!-- ESM -->
<script type="module">
  import * as csstree from '';
  import * as csstree from '';

<!-- IIFE with an export to global -->
<script src=""></script>
<script src=""></script>

Top level API

API map





Last updated on 14 Dec 2022

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Socket installs a GitHub app to automatically flag issues on every pull request and report the health of your dependencies. Find out what is inside your node modules and prevent malicious activity before you update the dependencies.


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