RegexLab

About RegexLab

RegexLab is a free online regex tester built for Google Analytics 4 analysts who need to check patterns before pasting them into GA4 filters, explorations, segments or audiences. It highlights every match against sample text as you type, so you can confirm a page path or event name pattern works before it goes live.

The tool targets analysts and marketers who work with GA4 every week. It offers ready-made examples for page paths, event names and locale prefixes, plus a token-by-token explanation panel, a substitution preview and flag toggles for global, case-insensitive, multiline, dotall, unicode and sticky matching. The site explains GA4's full-match behaviour and RE2 syntax limits, which helps explain why a pattern that looks right may return no data.

Matching runs locally in the browser using the native JavaScript RegExp engine, so test data is not sent to a server and the page works offline once loaded. Accounts and sign-up are not required, and the tool is supported by ads.