Domain Validator

The Domain Validator checks whether a string is a syntactically valid domain name under the rules laid out in RFC 1034, RFC 1035 and RFC 5891 (Internationalized Domain Names). It catches the most common mistakes in a domain string: length limits per label (max 63 characters) and total (max 253 characters), disallowed characters, leading or trailing hyphens, empty labels, invalid TLDs and improperly encoded Unicode.

Developers use this tool when validating user input in signup forms, DNS zone editors, email address validation flows, contact forms and CSV imports. Instead of hand-rolling a regex that misses edge cases (single-character subdomains, IDN punycode, emoji domains, long labels), you get a fast, standards-accurate answer. This matters because a lax regex accepts junk that breaks downstream systems, while a too-strict regex rejects legitimate domains such as `xn--e1afmkfd.xn--p1ai` or `1.example.com`.

The validator is also a good sanity check when auditing a bulk domain list — deduplicate, lowercase and normalize entries before feeding them into WHOIS, DNS or SSL scans.