Regex Tester
Test a regular expression against sample text — live match highlighting, capture groups and a replace preview. Runs on your browser's own regex engine; nothing is uploaded.
This uses the browser's native RegExp — close to PCRE, but not identical (e.g. no \A, lookbehind support varies).
A regular expression describes a search pattern. Type one above and it runs live against your test string: matches are highlighted, the count updates, capture groups from the first match are listed, and the replace box previews String.replace (use $1, $2 or $<name> for groups).
This uses your browser's native JavaScript regex engine, so it's the exact behaviour your JS code will get — but it differs slightly from PCRE/Python (flag set is gimsuy, some lookbehind/Unicode-property support depends on your browser). Nothing is sent anywhere; an invalid pattern just shows the engine's error.