Regex Tester & Validator

Matches IPv6-style addresses at the start of a line (multiline mode), built from hexadecimal groups of 1-4 digits separated by colons, including compressed sections using consecutive colons (::). The trailing lookahead (?= ) requires a space after the match, making it well-suited for parsing log files where an IPv6 address is followed by whitespace, such as Apache or nginx access logs. Note it is a loose validator and may accept some malformed addresses.