psl (Public Suffix List)

psl is a JavaScript domain name parser based on the Public Suffix List.

This implementation is tested against the test data hosted by Mozilla and kindly provided by Comodo.

Cross browser testing provided by

What is the Public Suffix List?

The Public Suffix List is a cross-vendor initiative to provide an accurate list of domain name suffixes.

The Public Suffix List is an initiative of the Mozilla Project, but is maintained as a community resource. It is available for use in any software, but was originally created to meet the needs of browser manufacturers.

A "public suffix" is one under which Internet users can directly register names. Some examples of public suffixes are ".com", ".co.uk" and "pvt.k12.wy.us". The Public Suffix List is a list of all known public suffixes.

Source: https://publicsuffix.org

Installation

This module is available both for Node.js and the browser. See below for more details.

Node.js

This module is tested on Node.js v8, v10, v12, v14, v16, v18, v20 and v22. See .github/workflows/node.js.yml.

npm install psl

ESM

From version v1.13.0 you can now import psl as ESM.

import psl from 'psl';

CommonJS

If your project still uses CommonJS, you can continue importing the module like in previous versions.

const psl = require('psl');

Browser

Using a bundler

If you are using a bundler to build your app, you should be able to import and/or require the module just like in Node.js.

ESM (using a CDN)

In modern browsers you can also import the ESM directly from a CDN. For example:

import psl from 'https://unpkg.com/psl@latest/dist/psl.mjs';

UMD / CommonJS

Finally, you can still download dist/psl.umd.cjs and include it in a script tag.

This script is bundled and wrapped in a umd wrapper so you should be able to use it standalone or together with a module loader.

The script is also available on most popular CDNs. For example:

• https://unpkg.com/psl@latest/dist/psl.umd.cjs

API

psl.parse(domain)

Parse domain based on Public Suffix List. Returns an Object with the following properties:

• tld: Top level domain (this is the public suffix).
• sld: Second level domain (the first private part of the domain name).
• domain: The domain name is the sld + tld.
• subdomain: Optional parts left of the domain.

Examples

Parse domain without subdomain:

import psl from 'psl';

const parsed = psl.parse('google.com');
console.log(parsed.tld); // 'com'
console.log(parsed.sld); // 'google'
console.log(parsed.domain); // 'google.com'
console.log(parsed.subdomain); // null

Parse domain with subdomain:

import psl from 'psl';

const parsed = psl.parse('www.google.com');
console.log(parsed.tld); // 'com'
console.log(parsed.sld); // 'google'
console.log(parsed.domain); // 'google.com'
console.log(parsed.subdomain); // 'www'

Parse domain with nested subdomains:

import psl from 'psl';

const parsed = psl.parse('a.b.c.d.foo.com');
console.log(parsed.tld); // 'com'
console.log(parsed.sld); // 'foo'
console.log(parsed.domain); // 'foo.com'
console.log(parsed.subdomain); // 'a.b.c.d'

psl.get(domain)

Get domain name, sld + tld. Returns null if not valid.

Examples

import psl from 'psl';

// null input.
psl.get(null); // null

// Mixed case.
psl.get('COM'); // null
psl.get('example.COM'); // 'example.com'
psl.get('WwW.example.COM'); // 'example.com'

// Unlisted TLD.
psl.get('example'); // null
psl.get('example.example'); // 'example.example'
psl.get('b.example.example'); // 'example.example'
psl.get('a.b.example.example'); // 'example.example'

// TLD with only 1 rule.
psl.get('biz'); // null
psl.get('domain.biz'); // 'domain.biz'
psl.get('b.domain.biz'); // 'domain.biz'
psl.get('a.b.domain.biz'); // 'domain.biz'

// TLD with some 2-level rules.
psl.get('uk.com'); // null);
psl.get('example.uk.com'); // 'example.uk.com');
psl.get('b.example.uk.com'); // 'example.uk.com');

// More complex TLD.
psl.get('c.kobe.jp'); // null
psl.get('b.c.kobe.jp'); // 'b.c.kobe.jp'
psl.get('a.b.c.kobe.jp'); // 'b.c.kobe.jp'
psl.get('city.kobe.jp'); // 'city.kobe.jp'
psl.get('www.city.kobe.jp'); // 'city.kobe.jp'

// IDN labels.
psl.get('食狮.com.cn'); // '食狮.com.cn'
psl.get('食狮.公司.cn'); // '食狮.公司.cn'
psl.get('www.食狮.公司.cn'); // '食狮.公司.cn'

// Same as above, but punycoded.
psl.get('xn--85x722f.com.cn'); // 'xn--85x722f.com.cn'
psl.get('xn--85x722f.xn--55qx5d.cn'); // 'xn--85x722f.xn--55qx5d.cn'
psl.get('www.xn--85x722f.xn--55qx5d.cn'); // 'xn--85x722f.xn--55qx5d.cn'

psl.isValid(domain)

Check whether a domain has a valid Public Suffix. Returns a Boolean indicating whether the domain has a valid Public Suffix.

Example

import psl from 'psl';

psl.isValid('google.com'); // true
psl.isValid('www.google.com'); // true
psl.isValid('x.yz'); // false

Testing and Building

There are tests both for Node.js and the browser (using Playwright and BrowserStack).

# Run tests in node.
npm test
# Run tests in browserstack.
npm run test:browserstack

# Update rules from publicsuffix.org
npm run update-rules

# Build ESM, CJS and UMD and create dist files
npm run build

Feel free to fork if you see possible improvements!

Acknowledgements

• Mozilla Foundation's Public Suffix List
• Thanks to Rob Stradling of Comodo for providing test data.
• Inspired by weppos/publicsuffix-ruby

License

The MIT License (MIT)

Copyright (c) 2014-2024 Lupo Montero

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.