Domain Syntax Validator
Enter a domain name and check it against the DNS naming rules — this checks syntax only, it doesn't look up whether the domain is registered or actually exists.
About this tool
DNS labels (the parts between dots) can be up to 63 characters, use only letters, digits and hyphens, and can't start or end with a hyphen. Hyphens in the third and fourth positions are reserved for the xn-- prefix used by internationalised names. The whole name can be up to 253 characters, and the top-level domain can't be all numbers. A trailing dot (example.com.) is allowed.
Internationalised domains such as bücher.de are converted to the ASCII form DNS actually uses (xn--bcher-kva.de) before checking, and the result shows it. If you paste a full URL or an email address, just the domain part is checked. This tool checks syntax only: it doesn't look up DNS or a registrar, so a valid result doesn't mean the domain exists or is available, and it doesn't check that the top-level domain is real.