Public Suffix List

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The Public Suffix List is a catalog of certain Internet domain names. The term is also known by the form effective top-level domain (eTLD).[1] The Mozilla Foundation maintains suffix list for the security and privacy policies of its Firefox web browser, though it is available for other uses under the Mozilla Public License (MPL).


The list is used by Mozilla browsers (Firefox), by Google in Chrome and Chromium projects on certain platforms,[2] and by Opera.[3]

According to Mozilla,[4]

A "public suffix" is one under which Internet users can directly register names. Some examples of public suffixes are ".com", "" and "".

While com, uk, and us are top-level domains (TLDs), Internet users cannot always register the next level of domain, such as "" or "", because these may be controlled by domain registrars. By contrast, users can register second level domains within com, such as, because registrars control only the top level. The Public Suffix List is intended to enumerate all domain suffixes controlled by registrars.[5]

Some uses for the list are:

  • Avoiding "supercookies", HTTP cookies set for high-level domain name suffixes. In other words, a page at might normally have access to cookies at, but should be walled off from cookies at, since the latter two domains could be registered by different owners.
  • Finding DMARC policy records for email subdomains.
  • Highlighting the most important part of a domain name in the user interface.
  • Improving the sorting of browser history entries by site.


  1. ^ "Public Suffix List - MozillaWiki". Retrieved 18 May 2017.
  2. ^ "364745 - Treat PSL matching consistently across all platforms". Retrieved 18 May 2017.
  3. ^ "Cookies and the Public Suffix List". Heroku. 11 October 2013. Retrieved 19 January 2014.
  4. ^ "Public Suffix List". Retrieved 18 May 2017.
  5. ^ Murray Kucherawy (13 April 2015). "Additional Background Information for dbound". IETF working group. The PSL is maintained by a web browser producer and is kept current by volunteers on a best-effort basis. It contains a list of points in the hierarchical namespace at which registrations take place, and is used to identify the boundary between so-called "public" names (below which registrations can occur, such as ".com" or "") and the private names (organizational names) that domain registrars create within them.

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