Regex Tester & Explainer

Enter a regular expression, toggle flags, and type a test string to see every match and capture group highlighted live. This regex tester lists each match with its index and groups, and - uniquely - gives a plain-English, token-by-token explanation of what your pattern actually does, so you can learn regex while you debug it.

Matching runs inside a sandboxed worker with a time limit, so even a pathological, catastrophic-backtracking pattern can never freeze the page - it's safely rejected with a clear message. Invalid expressions show a friendly error instead of crashing. Everything runs in your browser with no uploads and no signup, and it works offline once loaded. Build, test, and finally understand your regex in one place.