Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Check whether a domain name follows valid label formatting rules.
Enter a domain name to check its label format. This does not check DNS registration.
This tool checks whether a domain name follows valid formatting rules for each dot-separated label -- length, allowed characters, and hyphen placement -- per the domain naming standard. It's a format check only; it doesn't verify the domain is registered or resolvable via DNS.
Enter a domain name. The result shows whether it's valid, and if not, which label and rule it violates.
Each label (the text between dots) must be 1-63 characters, containing only letters, digits, and hyphens, with no leading or trailing hyphen. The overall domain must be under 253 characters and contain at least one dot (a top-level domain).
For internationalized (non-ASCII) domain names, see the Punycode Converter.
A single label may be between 1 and 63 characters, so a 63-character label passes and a 64-character one fails. The entire domain, including dots, must be no longer than 253 characters. The error message names the first label that breaks a rule, which makes it easy to find the problem in a long domain with many subdomains.
The tool only inspects shape. It does not know whether the last label is a real top-level domain, so example.zzzz and even example.123 pass. It does not check whether the name is registered, whether it has DNS records or whether it is reserved. A domain that is valid in format can still be unavailable or unregistered. To find out about registration or ownership, use a registrar search or a WHOIS lookup; to see whether it points to a server, use a DNS lookup tool.
Domains with accented letters or non-Latin scripts are stored in DNS in an ASCII form that begins with xn--. Convert your name to that punycode form first, then validate it here; the xn-- prefix and the hyphen pair inside it are accepted. Pasting the accented characters directly will fail, since only ASCII letters, digits and hyphens are allowed.
No -- this checks formatting rules only; confirming registration status requires a WHOIS lookup or DNS query, which this offline tool doesn't perform.
It's a rule from the original domain naming standard (RFC 1035) -- hyphens are allowed within a label but not at either end, to avoid ambiguity with other naming conventions.
Not directly -- an internationalized domain needs to be converted to its ASCII Punycode form first (see the Punycode Converter) before this ASCII-based validator can check it.
Yes. Domain names are not case sensitive, and the tool lowercases the input before checking.
A trailing dot is technically used in DNS to mark a fully qualified name, but here it creates an empty label, which the tool treats as invalid. Remove it and re-check.
No. Any label that follows the character rules is accepted as the last part, so a made-up ending can still pass.
Each label can be up to 63 characters, and the whole domain up to 253 characters.
Reference: MDN Web Docs