Regex tester
Test regular expressions with real-time match highlighting.
Type a regular expression, pick the flags and watch matches highlight in the text as you type, with the first match’s capture groups listed below. It uses the browser’s own JavaScript regex engine — the exact behavior your code will have in production.
Frequently asked questions
Which regex "flavor" is used?
JavaScript’s (ECMAScript), executed by the browser itself. Features like lookbehind and named groups work in modern browsers; PCRE/Python-only syntax (like (?P<name>)) does not.
What do the g, i, m and s flags do?
g finds all matches (not just the first); i ignores case; m makes ^ and $ work per line; s makes the dot (.) also match line breaks.
Why does my regex freeze other online testers?
Patterns with catastrophic backtracking (e.g. (a+)+b) explode execution time. Here processing is local and capped at 2,000 matches — and your text is never uploaded, which also removes size limits.