Regex Explainer

How it works

• Everything runs client-side — no network request, no upload, no server round-trip.
• The breakdown uses a small hand-written parser covering groups (capturing, named, non-capturing), lookaround, character classes, quantifiers, anchors, escapes, alternation, and backreferences.
• Match testing uses your browser's real RegExp engine, so results reflect exactly how the pattern behaves in JavaScript.
• Advanced or unusual syntax (some Unicode property escapes, multi-digit backreferences) may not get a full explanation — match testing still works even when the breakdown can't.
• Very complex patterns tested against long strings can be slow — regex engines can have poor worst-case performance ("catastrophic backtracking").
• Click the ⌖ button on any clause card to highlight that exact piece back in the pattern field.