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CSSTree Validator

CSS Validator built on CSSTree.

Technically, the package utilizes the capabilities of CSSTree to match CSS syntaxes to various parts of your code and generates a list of errors, if any.

Note: If csstree-validator produces false positives or false negatives, such as unknown properties or invalid values for a property, please report the issue to the CSSTree issue tracker.

Note: CSSTree currently doesn't support selector syntax matching; therefore, csstree-validator doesn't support it either. Support for selector validation will be added once it is available in CSSTree.

Installation

Install the package via npm:

npm install csstree-validator

Usage

You can validate a CSS string or a CSSTree AST:

import { validate } from 'csstree-validator';
// For CommonJS:
// const { validate } = require('csstree-validator');

const filename = 'demo/example.css';
const css = '.class { pading: 10px; border: 1px super red }';

console.log(validate(css, filename));
// Output:
// [
//   SyntaxError [SyntaxReferenceError]: Unknown property `pading` {
//     reference: 'pading',
//     property: 'pading',
//     offset: 9,
//     line: 1,
//     column: 10
//   },
//   SyntaxError [SyntaxMatchError]: Mismatch {
//     message: 'Invalid value for `border` property',
//     rawMessage: 'Mismatch',
//     syntax: '<line-width> || <line-style> || <color>',
//     css: '1px super red',
//     mismatchOffset: 4,
//     mismatchLength: 5,
//     offset: 35,
//     line: 1,
//     column: 36,
//     loc: { source: 'demo/example.css', start: [Object], end: [Object] },
//     property: 'border',
//     details: 'Mismatch\n' +
//       '  syntax: <line-width> || <line-style> || <color>\n' +
//       '   value: 1px super red\n' +
//       '  ------------^'
//   }
// ]

Alternatively, you can use helper functions to validate a file or directory and utilize one of the built-in reporters:

import { validateFile, reporters } from 'csstree-validator';

const result = validateFile('./path/to/style.css');
console.log(reporters.checkstyle(result));

Validation Methods

  • validate(css, filename)
  • validateAtrule(node)
  • validateAtrulePrelude(atrule, prelude, preludeLoc)
  • validateAtruleDescriptor(atrule, descriptor, value, descriptorLoc)
  • validateDeclaration(property, value, valueLoc)
  • validateRule(node)

Helpers

Note: Helpers are not available in browser environments as they rely on Node.js APIs.

All helper functions return an object where the key is the path to a file and the value is an array of errors. The result object is iterable (has Symbol.iterator) and can be used with for...of loops or the spread operator.

Example:

const result = validateFile('path/to/file.css');

for (const [filename, errors] of result) {
  // Process errors
}

Available helper functions:

  • validateString(css, filename)
  • validateDictionary(dictionary)
  • validateFile(filename)
  • validatePath(searchPath, filter)
  • validatePathList(pathList, filter)

Reporters

CSSTree Validator provides several built-in reporters to convert validation results into different formats:

  • console – Human-readable text suitable for console output.

  • json – Converts errors into a unified JSON array of objects:

    type ErrorEntry = {
  name: string; // Filename
  line: number;
  column: number;
  atrule?: string;
  descriptor?: string;
  property?: string;
  message: string;
  details?: any;
}

  • checkstyle – Checkstyle XML report format:

    <?xml version="1.0" encoding="utf-8"?>
<checkstyle version="4.3">
  <file name="{filename}">
    <error line="{line}" column="{column}" severity="error" message="{message}" source="csstree-validator" />
  </file>
</checkstyle>

  • gnu – GNU error log format:

    "FILENAME":LINE.COLUMN: error: MESSAGE
"FILENAME":START_LINE.COLUMN-END_LINE.COLUMN: error: MESSAGE

Example usage:

import { validate, reporters } from 'csstree-validator';

const css = '.class { padding: 10px; color: red; }';
const result = validate(css, 'example.css');

console.log(reporters.json(result));
// Output:
// [
//   { "name": 'example.css', ... },
//   { "name": 'example.css', ... },
//   ...
// ]

Browser Usage

CSSTree Validator can be used in browser environments using the available bundles:

  • IIFE Bundle (dist/csstree-validator.js) – Minified IIFE with csstreeValidator as a global variable.

    <script src="node_modules/csstree-validator/dist/csstree-validator.js"></script>
<script>
  const errors = csstreeValidator.validate('.some { css: source }');
</script>

  • ES Module (dist/csstree-validator.esm.js) – Minified ES module.

    <script type="module">
  import { validate } from 'csstree-validator/dist/csstree-validator.esm.js';

  const errors = validate('.some { css: source }');
</script>

You can also use a CDN service like unpkg or jsDelivr. By default, the ESM version is exposed for short paths. For the IIFE version, specify the full path to the bundle:

<!-- ESM -->
<script type="module">
  import * as csstreeValidator from 'https://cdn.jsdelivr.net/npm/csstree-validator';
  // or
  import * as csstreeValidator from 'https://unpkg.com/csstree-validator';
</script>

<!-- IIFE with csstreeValidator as a global -->
<script src="https://cdn.jsdelivr.net/npm/csstree-validator/dist/csstree-validator.js"></script>
<!-- or -->
<script src="https://unpkg.com/csstree-validator/dist/csstree-validator.js"></script>

Note: Helpers are not available in the browser version.

Command-Line Interface (CLI)

Install globally via npm:

npm install -g csstree-validator

Run the validator on a CSS file:

csstree-validator /path/to/style.css

Display help:

csstree-validator -h
Usage:

    csstree-validator [fileOrDir] [options]

Options:

    -h, --help                     Output usage information
    -r, --reporter <nameOrFile>    Output formatter: console (default), checkstyle, json, gnu
                                   or <path to a module>
    -v, --version                  Output version

Custom Reporters

In addition to the built-in reporters, you can specify a custom reporter by providing the path to a module or package. The module should export a single function that takes the validation result object and returns a string:

export default function(result) {
  let output = '';

  for (const [filename, errors] of result) {
    // Generate custom output
  }

  return output;
}

// For CommonJS:
// module.exports = function(result) { ... }

The reporter option accepts:

  • ESM Module – Full path to a file with a .js extension.
  • CommonJS Module – Full path to a file with a .cjs extension.
  • ESM Package – Package name or full path to a module within the package.
  • CommonJS Package – Package name or path to a module within the package.
  • Dual Package – Package name or full path to a module within the package.

The resolution algorithm checks the reporter value in the following order:

  1. If it's a path to a file (relative to process.cwd()), use it as a module.
  2. If it's a path to a package module (relative to process.cwd()), use the package's module.
  3. Otherwise, the value should be the name of one of the predefined reporters, or an error will be raised.

Integrations

Plugins that use csstree-validator:

License

MIT