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Regex Tester
Type a pattern, toggle flags, paste your text — every match highlights instantly with its numbered and named capture groups. Your pattern and text never leave your device.
Test your regular expression
Compiled by your browser's own RegExp engine — the same flavour as JavaScript, Node.js, Chrome and Edge.
How it works
Type between the slashes, then tap the flag chips for g, i, m, s, u or y.
Live re-evaluation is debounced while you type, so even long logs stay smooth.
Alternating highlight bands, index and length per match, plus every numbered and named capture group.
Regex cheatsheet
Tap a token to insert it at the caret in the pattern box — the preview updates instantly.
FAQ
Is my pattern sent to a server?
No. Everything — compiling, matching, highlighting and the JSON dump — runs in your browser with JavaScript's native RegExp object. There is no upload step and no analytics on your text.
Which regex flavour is this?
JavaScript (ECMAScript). That is what browsers, Node.js, Deno and Bun use, and it covers lookahead, lookbehind, named groups, unicode property escapes and the s/u/y flags. PCRE-only syntax such as (?&name) or atomic groups is not supported.
Why do I only get one match?
Turn on the g (global) flag. Without it the engine stops at the first match — the tester mirrors that behaviour exactly.
How many matches can it handle?
Up to 200,000 characters of test string and 2,000 matches per run; the list and JSON preview the first 200 so the page never stalls on giant logs.
What does an empty match mean?
Patterns like or a* can match zero characters. Those are drawn as a thin indigo bar so you can still see where they landed, and the walker steps past them so it never loops forever.