RegExLib.com - The first Regular Expression Library on the Web!

Checks domain names. This validates domains based on latest specifications (RFCs 952 and 1123 dealing with hostnames and RFC 1035 dealing with domain name system requirements) except that it only includes realistic fully-qualified domains: 1. requires at least one subdomain 2. allows shortest top-level domains like "ca", and "museum" as longest. Other validation rules: 1. Labels/parts should be seperated by period. 2. Each label/part has maximum of 63 characters. 3. First and last character of label must be alphanumeric, other characters alphanumeric or hyphen. 4. Does not check maxlength of domain which incidentally is 253 characters of text (255 binary representation). For a regular expression that matches ALL domains: ^([a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.)*[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?$