What is an eTLD + 1?
In short, an eTLD + 1 is the part of the web address that tells you who owns a website. What does that mean and how exactly can you find it? This post answers these questions.
#0 what is a domain?
The domain is the part of a website address after the protocol (
https://) and before the next
slash. In a URL like
https://jfhr.me/what-is-an-etld-+-1 , the domain is
#1 what is a TLD?
A domain consists of one or more parts separated by dots. The TLD is the last part. In the domain
jfhr.me , the
me is the TLD.
#2 what is an eTLD?
The eTLD consists of the last n parts of a domain that are shared between multiple sites from different owners.
www.google.com , the
com is the TLD and also the eTLD - because there are many
different pages with different owners ending in
com , but all pages ending in
belong to google. In
www.google.co.uk , the TLD is
uk , but the eTLD is
, because there are many different pages with different owners ending in
#3 what is an eTLD + 1?
The eTLD + 1 is the eTLD plus one more domain part. By definition, the eTLD + 1 and all pages below it belong to the
same person or organization. For example,
google.com is a eTLD + 1, because everything below it (like
drive.google.com ) belong google.
Schematic diagram of TLD, eTLD, and eTLD + 1.
#4 why does it matter?
There is a list called the public suffix list which aims to list all eTLDs on the internet. Browser
use it in different ways, but maybe the most important is to restrict cookies. You've probably heard of cookies,
they are small pieces of information that websites can store in your browser. Every cookie is associated with a
domain, and it can be accessed by that domain and all domains below it. When you visit
, it can set a cookie for
google.co.uk , and when you later visit
it can still read that cookie.
www.google.co.uk can't set a cookie for just
co.uk ! Because that is an
eTLD, so it doesn't have a single owner. If you set a cookie there, almost all British websites would be able to
read it, which would be terrible for your security and privacy.
You can find the public suffix list here: https://publicsuffix.org/ and under "Learn more" there's also more background.