About this tool

RegexLab is a free online regex tester built around real analytics work: testing Google Analytics 4 page path, event and filter regex before pasting them into GA4. It runs entirely client-side, so no data ever leaves your device, and requires no login. GA4 uses full-match semantics and the RE2 engine (no lookahead or backreferences), which is why most regexes that work everywhere else silently return zero rows in GA4. RegexLab ships with reference guides covering a GA4 pattern cheat sheet, page path regex, event filter recipes and an RE2 vs PCRE migration reference.