Regex Tester
Test JavaScript regular expressions against your text with live highlighting, a table of matches and capture groups, and an optional replace preview.
Free · No upload · 100% on your device
How to use Regex Tester
- Type or paste your code or data, or open a file.
- Choose the settings in the side panel. The result updates as you type.
- Copy the result or download it as a file.
Private by design. Everything you type, open or record is processed in this browser tab and is never uploaded to KittySuite.
About Regex Tester
Patterns use JavaScript syntax, the same as in browsers and Node.js, including named groups (?<name>…) and lookbehind. Each test runs in a separate worker and is stopped after two seconds, so a pattern with catastrophic backtracking cannot freeze the page.
Everything runs in this browser tab: your text is never uploaded or stored, and the result updates as you type. It keeps working offline once the page has loaded.
Regex Tester: frequently asked questions
How do I test a regular expression?
Type the pattern and paste your text. Matches are highlighted live, with a table of matches and capture groups.
Which regex syntax is used?
JavaScript, the same as browsers and Node.js, including named groups (?<name>…) and lookbehind. Flags g, i, m, s, u and y can be switched on.
Can I test a replacement?
Yes. Turn on “Preview a replacement” and use $1, $2 or named groups in the replacement.
Will a bad pattern freeze the page?
No. Each test runs in a separate worker and is stopped after two seconds, so catastrophic backtracking cannot lock up the tab.