// free · runs in your browser · nothing uploaded
Regex Tester
Test JavaScript regular expressions live: every match highlighted, numbered and named groups, all flags, and replace with $1 or $<name>. Slow patterns are stopped so your browser never freezes.
📚 Official sources: MDN regular expressions
We build every tool from the official rules and re-check them when they change. Always confirm with the official source before you rely on a result.
🛠️ Spotted a mistake or an out-of-date rule? Tell us
Questions people ask
Which regex flavour does this use?+
JavaScript (ECMAScript), the same engine as Chrome and Node.js. It supports named groups (?<name>…), lookbehind, Unicode property escapes with the u flag, and the s (dotAll) flag.
What do the flags mean?+
g finds every match instead of the first, i ignores upper/lower case, m makes ^ and $ match at each line, s lets . match line breaks, and u turns on full Unicode support.
Why was my pattern stopped?+
Some patterns, such as nested quantifiers like (a+)+, can take exponential time on certain text (catastrophic backtracking). The tester runs each pattern in a separate worker and stops it after 1.5 seconds so your page never freezes.
How do I use groups in the replacement?+
Use $1, $2 … for numbered groups, $<name> for named groups and $& for the whole match.