Public Suffix List and IANA Root Zone Database based Domain parsing implemented in PHP.

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5.7.2 2020-10-26 06:41 UTC


PHP Domain Parser is domain parser implemented in PHP.

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While there are plenty of excellent URL parsers and builders available, there are very few projects that can accurately parse a domain into its component subdomain, registrable domain, second level domain and public suffix parts.

Consider the domain In this domain, the public suffix portion is, the registrable domain is, the subdomain is www and the second level domain is pref.
You can't regex that.

PHP Domain Parser is compliant around:

  • accurate Public Suffix List based parsing.
  • accurate Root Zone Database parsing.



$ composer require jeremykendall/php-domain-parser:^6.0

System Requirements

You need:

  • PHP >= 7.4 but the latest stable version of PHP is recommended
  • the intl extension


If you are upgrading from version 5 please check the upgrading guide for known issues.

Resolving Domains

To effectively resolve a domain you need a public source. This library can resolve a domain against:

Resolving the Domain against the Public Suffix List

Using the Pdp\Rules class you can resolve a domain as a Pdp\ResolvedDomain object against the Public Suffix List as shown below:

use Pdp\Rules;

$rules = Rules::fromPath('/path/to/cache/public-suffix-list.dat');

$result = $rules->resolve('www.PreF.OkiNawA.jP');
echo $result->domain()->toString();            //display '';
echo $result->subDomain()->toString();         //display 'www';
echo $result->secondLevelDomain();             //display 'pref';
echo $result->registrableDomain()->toString(); //display '';
echo $result->publicSuffix()->toString();      //display '';
$result->publicSuffix()->isICANN();            //returns true;

In case of an error an exception which implements the Pdp\CannotProcessHost is thrown.

You can modify the returned Pdp\ResolvedDomain instance using the following methods:

use Pdp\Rules;

$rules = Rules::fromPath('/path/to/cache/public-suffix-list.dat');

$result = $rules->resolve('');
$altResult = $result

echo $result->domain()->toString(); //display '';
$result->publicSuffix()->isKnown(); //returns true;

echo $altResult->domain()->toString(); //display '';
$altResult->publicSuffix()->isKnown(); //returns false;

The public suffix method isKnown will always return false if your input is not a PublicSuffix object in which case the method may return true. For more information, see the following section.

Public Suffix List Sections

The Public Suffix List is organized in sections. This library can give you access to this information via its public suffix object.

use Pdp\Rules;

$rules = Rules::fromPath('/path/to/cache/public-suffix-list.dat');

$publicSuffix = $rules->resolve('')->publicSuffix();

echo $publicSuffix->domain()->toString(); //display '';
$publicSuffix->isICANN();                 //will return false
$publicSuffix->isPrivate();               //will return true
$publicSuffix->isKnown();                 //will return true

The public suffix state depends on its value:

  • isKnown returns true if the value is present in the PSL.
  • isICANN returns true if the value is present in the PSL ICANN section.
  • isPrivate returns true if the value is present in the PSL private section.

If the value is not present in the PSL all the methods above will return false.

Rules::resolve will always return a ResolvedDomain even if the domain syntax is invalid or no entry was found in the desired section. To work around the limitation of the official algorithm, this library exposes more strict methods:

  • Rules::getCookieDomain
  • Rules::getICANNDomain
  • Rules::getPrivateDomain

These methods act and resolve the domain against the PSL just like the resolve method but will throw an exception if no valid effective TLD is found in the respective PSL section or if the submitted domain is invalid.

use Pdp\Rules;

$rules = Rules::fromPath('/path/to/cache/public-suffix-list.dat');

// will throw because `.unknownTLD` is not part of the ICANN section

// will not throw because the domain syntax is correct.

// will throw because no public suffix can be determined

// will return a Nullable Resolved domain

Last but not least it is possible to instantiate a PublicSuffix object using one of it's named constructor:

use Pdp\PublicSuffix;

$icann = PublicSuffix::fromICANN('');
$private = PublicSuffix::fromPrivate('');
$unknown = PublicSuffix::fromUnknown('');

Using a PublicSuffix object instead of a string or null with ResolvedDomain::withPublicSuffix will ensure that the returned value will always contain the correct information regarding the public suffix resolution.

Resolving the Domain against the IANA Root Zone Database

While the Public Suffix List is a community based list, the package provides access to the Top Level domain information given by the IANA website to always resolve top domain against all registered TLD even the new ones.

use Pdp\TopLevelDomains;

$iana = TopLevelDomains::fromPath('/path/to/cache/tlds-alpha-by-domain.txt');

$result = $iana->resolve('www.PreF.OkiNawA.jP');
echo $result->domain()->toString();            //display '';
echo $result->publicSuffix()->toString();      //display 'jp';
echo $result->secondLevelDomain();             //display 'okinawa';
echo $result->registrableDomain()->toString(); //display '';
echo $result->subDomain()->toString();         //display 'www.pref';

In case of an error an exception which extends Pdp\CannotProcessHost is thrown.


You should never use resolve domain name this way in production, without, at least, a caching mechanism to reduce PSL downloads.

Using the Public Suffix List to determine what is a valid domain name and what isn't is dangerous, particularly in these days when new gTLDs are arriving at a rapid pace.

If you are looking to know the validity of a Top Level Domain, the IANA Root Zone Database is the proper source for this information or alternatively consider using directly the DNS.

If you must use this library for any of the above purposes, please consider integrating an updating mechanism into your software.

Accessing and processing Domain labels

If you are interested into manipulating the domain labels without taking into account the Effective TLD, the library provides a Domain object tailored for manipulating domain labels. You can access the object using the following methods:

  • the ResolvedDomain::domain method
  • the PublicSuffix::domain method
  • from ResolvedDomain::subDomain method
  • the ResolvedDomain::registrableDomain returns a ResolvedDomain

Domain objects usage are explain in the next section.

/** @var  Rules $rules */
$result = $rules->resolve('');
$domain = $rules->resolve('')->domain();
echo $domain->toString(); // display ''
count($domain);           // returns 4
$domain->labels();        // returns ['uk', 'co', 'bbc', 'www'];
$domain->label(-1);       // returns 'www'
$domain->label(0);        // returns 'uk'
foreach ($domain as $label) {
   echo $label, PHP_EOL;
// display 
// uk
// co
// bbc
// www

$publicSuffixDomain = $result->publicSuffix()->domain();
$publicSuffixDomain->labels(); // returns ['uk', 'co']

You can also add or remove labels according to their key index using the following methods:


/** @var  Rules $rules */
$domain = $rules->resolve('www.ExAmpLE.cOM')->domain();

$newDomain = $domain
    ->withLabel(1, 'com')  //replace 'example' by 'com'
    ->withoutLabel(0, -1)  //remove the first and last labels

echo $domain->toString();    // display ''
echo $newDomain->toString(); // display ''

WARNING: Because of its definition, a domain name can be null or a string.

To distinguish this possibility the object exposes two (2) formatting methods Domain::value which can be null or a string and Domain::toString which will always cast the domain value to a string.

use Pdp\Domain;

$nullDomain = Domain::fromIDNA2008(null);
$nullDomain->value();    // returns null;
$nullDomain->toString(); // returns '';

$emptyDomain = Domain::fromIDNA2008('');
$emptyDomain->value();    // returns '';
$emptyDomain->toString(); // returns '';

ASCII and Unicode formats.

Domain names originally only supported ASCII characters. Nowadays, they can also be presented under a UNICODE representation. The conversion between both formats is done using the compliant implementation of UTS#46, otherwise known as Unicode IDNA Compatibility Processing. Domain objects expose a toAscii and a toUnicode methods which returns a new instance in the converted format.

/** @var  Rules $rules */
$unicodeDomain = $rules->resolve('bébé.be')->domain();
echo $unicodeDomain->toString(); // returns 'bébé.be'

$asciiDomain = $rules->resolve('')->domain();
echo $asciiDomain->toString();  // returns ''

$asciiDomain->toUnicode()->toString() === $unicodeDomain->toString(); //returns true
$unicodeDomain->toAscii()->toString() === $asciiDomain->toString();   //returns true

By default, the library uses IDNA2008 algorithm to convert domain name between both formats. It is still possible to use the legacy conversion algorithm known as IDNA2003.

Since direct conversion between both algorithms is not possible you need to explicitly specific on construction which algorithm you will use when creating a new domain instance via the Pdp\Domain object. This is done via two (2) named constructors:

  • Pdp\Domain::fromIDNA2008
  • Pdp\Domain::fromIDNA2003

At any given moment the Pdp\Domain instance can tell you whether:

  • the algorithm used for converting the domain is IDNA2008;
  • if the domain value is in ASCII mode or not;
use Pdp\Domain;

$domain = Domain::fromIDNA2008('faß.de');
echo $domain->value(); // display 'faß.de'
$domain->isIdna2008(); // returns true
$domain->isAscii();    // return false

$asciiDomain = $domain->toAscii(); 
echo $asciiDomain->value(); // display ''
$asciiDomain->isIdna2008(); // returns true
$asciiDomain->isAscii();    // returns true

$domain = Domain::fromIDNA2003('faß.de');
echo $domain->value(); // display ''
$domain->isIdna2008(); // returns false
$domain->isAscii();    // returns true

$asciiDomain = $domain->toAscii();
echo $asciiDomain->value(); // display ''
$asciiDomain->isIdna2008(); // returns false
$asciiDomain->isAscii();    // returns true

TIP: Always favor submitting a Pdp\Domain object for resolution rather that a string or an object that can be cast to a string to avoid unexpected format conversion errors/results. By default, and with lack of information conversion is done using IDNA 2008 rules.

Managing the package external resources

Depending on your application, the mechanism to store your resources may differ, nevertheless, the library comes bundle with a optional service which enables resolving domain name without the constant network overhead of continuously downloading the remote databases.

The interfaces defined under the Pdp\Storage namespace enable integrating a database managing system and provide an implementation example using PHP-FIG PSR interfaces.

The Pdp\Storage\PsrStorageFactory enables returning storage instances that retrieve, convert and cache the Public Suffix List and the IANA Root Zone Database using standard interfaces published by the PHP-FIG.

Instantiate Pdp\Storage\PsrStorageFactory

To work as intended, the Pdp\Storage\PsrStorageFactory constructor requires:

  • a PSR-16 Simple Cache implementing library.
  • a PSR-17 HTTP Factory implementing library.
  • a PSR-18 HTTP Client implementing library.

When creating a new storage instance you will require:

  • a $cachePrefix argument to optionally add a prefix to your cache index, default to the empty string;
  • a $ttl argument if you need to set the default $ttl, default to null to use the underlying caching default TTL;

The $ttl argument can be:

  • an int representing time in second (see PSR-16);
  • a DateInterval object (see PSR-16);
  • a DateTimeInterface object representing the date and time when the item will expire;

The package does not provide any implementation of such interfaces as you can find robust and battle tested implementations on packagist.

Refreshing the cached PSL and RZD data


For the purpose of this example we will use our PSR powered solution with:

  • Symfony HTTP Client as our PSR-18 HTTP client;
  • nyholm/psr7 which provide factories to create a PSR-7 objects;
  • Symfony Cache Component as our PSR-16 cache implementation;

We will cache both external sources for 24 hours in a PostgreSQL database.

You are free to use other libraries/solutions as long as they implement the required PSR interfaces.


use Pdp\Storage\PsrStorageFactory;
use Symfony\Component\HttpClient\Psr18Client;
use Symfony\Component\Cache\Adapter\PdoAdapter;
use Symfony\Component\Cache\Psr16Cache;

$pdo = new PDO(
$cache = new Psr16Cache(new PdoAdapter($pdo, 'pdp', 43200));
$client = new Psr18Client();
$cachePrefix = 'pdp_';
$cacheTtl = new DateInterval('P1D');
$factory = new PsrStorageFactory($cache, $client, $client);
$pslStorage = $factory->createPublicSuffixListStorage($cachePrefix, $cacheTtl);
$rzdStorage = $factory->createRootZoneDatabaseStorage($cachePrefix, $cacheTtl);

// if you need to force refreshing the rules 
// before calling them (to use in a refresh script)
// $pslStorage->delete(PsrStorageFactory::URL_PSL);
$rules = $pslStorage->get(PsrStorageFactory::URL_PSL);

// if you need to force refreshing the rules 
// before calling them (to use in a refresh script)
// $rzdStorage->delete(PsrStorageFactory::URL_RZD);
$tldDomains = $rzdStorage->get(PsrStorageFactory::URL_RZD);

Be sure to adapt the following code to your own application. The following code is an example given without warranty of it working out of the box.

You should use your dependency injection container to avoid repeating this code in your application.

Automatic Updates

It is important to always have an up to date Public Suffix List and Root Zone Database.
This library no longer provide an out of the box script to do so as implementing such a job heavily depends on your application setup. You can use the above example script as a starting point to implement such a job.


Please see CHANGELOG for more information about what has been changed since version 5.0.0 was released.


Contributions are welcome and will be fully credited. Please see CONTRIBUTING for details.


pdp-domain-parser has:

  • a PHPUnit test suite
  • a coding style compliance test suite using PHP CS Fixer.
  • a code analysis compliance test suite using PHPStan.

To run the tests, run the following command from the project folder.

$ composer test


If you discover any security related issues, please email instead of using the issue tracker.



The MIT License (MIT). Please see License File for more information.


Portions of the Pdp\Converter and Pdp\Rules are derivative works of the PHP registered-domain-libs. Those parts of this codebase are heavily commented, and I've included a copy of the Apache Software Foundation License 2.0 in this project.