Domains
Domain naming rules checker
Check a candidate name against the rule every ending shares, and then against that registry’s own stricter one.
Free, no accountIn your browser
The whole name, ending included - the ending is what decides which registry’s rules apply.
Result
Nothing to check yet
Type a candidate name with its ending and it is checked as you type.
What this is
Every ending shares one DNS label rule, and then its registry adds its own on top: this checker reads domain name rules by ending, holding a candidate name to the generic rule first and then to the registry’s published policy for whichever of the endings below it sits under.
The generic rule is the one DNS itself imposes: a label of at most 63 characters made of letters, digits and hyphens, a whole name of at most 253, and no hyphen at either end of a label. A name that breaks this cannot be registered anywhere, under any ending, by anyone.
A registry is free to narrow that rule, and several do. DENIC refuses a hyphen in both the third and fourth characters of a .de name; Afnic refuses the same pattern and will not sell a one- or two-character name under the French overseas endings; Nominet documents letters, digits and hyphens only. None of that is derivable from the generic rule - it has to be read off each registry’s own policy.
How to read the result
The findings come in the order the rules apply: the generic rule first, because fixing a name that no DNS zone can hold comes before anything a registry says, and then each stated rule of the registry behind the ending that was typed.
The facts panel names the exact label the registry rule was applied to, which matters for a second-level ending: under co.uk the registry’s rule is about the part in front of co.uk, not about the whole string.
A name that passes this check still needs the rest of a portfolio built around it; our guide Holding a domain portfolio: renewals, status codes and the names that attack yours covers what to track once it is registered, from renewal dates to lookalike names.
Common mistakes
What goes wrong most often, and how to tell.
- Taking a passing generic check as permissionA name can be a perfectly valid DNS label and still be refused at the counter. The generic rule knows nothing about a registry’s minimum length, its reserved words, or the hyphen patterns it keeps for internationalised names, which is why the registry’s own rule is checked separately here.
- Assuming an ending with no rules listed has noneAn ending absent from the table has simply not had its registry’s policy read and cited for this page. Treating that silence as permission is how a brand ends up with a shortlist of names its registry will not accept; the registry’s own policy page is the only authority on it.
- Counting an internationalised name in the characters you typedAn umlaut or an accent is stored by the registry as an xn-- A-label, and that encoded form is what the 63-character limit is measured against. A name that looks comfortably short in its own script can be well over the limit once encoded, so convert it before counting.
- Putting the hyphens wherever they look bestHyphens in the third and fourth position are reserved for the encoding of internationalised names, so a name like ab--cd is rejected outright by DENIC and Afnic however available it looks. Moving one hyphen a single character along clears the rule.
Questions
What people ask about this tool.
- No. A leading or trailing hyphen in a label is outside the generic DNS rule, so no registry will register it, and DENIC, Nominet and Afnic each restate that prohibition in their own policies as well.
- Because its registry’s own policy has not been read and cited for this page yet. Only the generic DNS rule was applied to it, and that is said in the result rather than quietly presented as the registry’s own rule.
- Convert it to its xn-- form with an IDN converter first, then check that form here: the registry applies its length and hyphen rules to the encoded label, not to the characters as they are typed or displayed.
- The one immediately in front of the registry’s ending, so for shop.co.uk the rules are applied to "shop". The facts panel names that label explicitly so there is no doubt about what was measured.
Sources
Every fixed value here comes from the provider’s own documentation. These pages change, so each says the day it was last read.
- DENIC, “DENIC Domain Guidelines” read 13 October 2026
- Nominet, “Registry field definitions and registrant types” read 13 October 2026
- Afnic, “Afnic Naming Policy, version of 6 July 2026” read 13 October 2026
- IETF, “RFC 1035: Domain Names - Implementation and Specification” read 13 October 2026
- IETF, “RFC 1123: Requirements for Internet Hosts - Application and Support” read 13 October 2026
Use it from the API
The same check, as one request.