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Editorial Team
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Asked: 2026-05-27T04:03:45+00:00

Given a URL, how do I extract the registered domain using the Public Suffix

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Given a URL, how do I extract the registered domain using the Public Suffix List (list of effective TLDs, e.g. this list)?

For instance, considering a.bg is a valid public suffix:

http://www.test.start.a.bg/hello.html -> start.a.bg 
http://test.start.a.bg/               -> start.a.bg
http://test.start.abc.bg/             -> abc.bg (.bg is the public suffix)

This cannot be done using simple string manipulation because the public suffix can consist of multiple levels depending on the TLD.

P.S. It doesn’t matter how I read the list (database or flat file), but the list should be accessible locally so I’m not always dependent on external services.

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1 Answer

  1. Editorial Team

    You can use parse_url() to extract the hostname, then use the library provided by regdom to determine the registered domain name (dn + eTLD). For example:

    require_once("effectiveTLDs.inc.php");
require_once("regDomain.inc.php");

$url =  'http://www.metu.edu.tr/dhasjkdas/sadsdds/sdda/sdads.html';
echo getRegisteredDomain(parse_url($url, PHP_URL_HOST));

    That will print out metu.edu.tr.

    Other examples I’ve tried:

    http://www.xyz.start.bg/hello   ->   start.bg
http://www.start.a.bg/world     ->   start.a.bg  (a.bg is a listed eTLD)
http://xyz.ma219.metu.edu.tr    ->   metu.edu.tr
http://www.google.com/search    ->   google.com
http://google.co.uk/search?asd  ->   google.co.uk

    UPDATE: These libraries have been moved to: https://github.com/leth/registered-domains-php

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