I'm trying to find a reliable list of countries whose country-code top-level domains require registrations to use an additional level, such as example.co.uk or example.com.br, instead of allowing example.uk or example.br directly. I found a table listing second-level domains, but I'm not sure whether that actually describes registration requirements or just common domain structures. Is there an authoritative source for these rules?
3 Answers
The Public Suffix List is useful for understanding domain boundaries, especially for cookies and user-controlled subdomains. However, it isn’t a definitive list of registration rules. For example, both .uk and .co.uk can appear as suffix boundaries even though registrations are possible at more than one level.
It depends on what you mean by “require.” Some registries have familiar structures like .co.uk, while also allowing direct registrations such as example.uk. Brazil has several organized options, including .com.br and .edu.br, but direct .br registrations may also be available in some cases. A list of second-level domains can show these naming patterns, but it doesn’t necessarily prove that the extra level is mandatory.
For authoritative information, start with IANA’s root zone database to identify the operator of each country-code domain, then check that registry’s published eligibility and registration policies. This is more reliable than a static table because rules can change over time, as happened with domains such as .uk, .nz, and .au.
That makes sense. I was looking for a simple table, but it sounds like I’ll need to verify the rules with each registry rather than treating the second-level-domain column as a complete answer.