Regex Tester

Notes: patterns run with JavaScript's regex engine, which is what you get in Node, browsers, and most modern tooling. The g flag finds all matches (without it you only get the first), i ignores case, m makes ^ and $ match per line, and s lets . cross newlines. The breakdown covers the constructs you meet day to day: classes, quantifiers, groups, anchors, alternation, and lookarounds. Library patterns are practical starting points, not perfect validators (fully RFC-compliant email regexes are famously enormous). Everything runs locally, nothing is uploaded.