Regex Tester & Validator

Matches lines of exactly six digits split into three two-digit pairs, where within each pair the second digit must differ from the first. This is enforced by capturing the first digit of each pair and using a negative lookahead with a backreference to reject immediate repetition. Useful for validating 6-digit codes or PINs where repeating adjacent digits inside each two-digit subset is disallowed; note it only checks within pairs, not across pair boundaries.