Regex Tester
Test regular expressions live — matches highlighted, count shown, errors handled safely.
The Regex Tester lets you write a pattern, set flags like g, i and m, and watch matches light up in your test text as you type. It shows the total match count and handles invalid patterns gracefully with a clear error. Perfect for building and debugging validation patterns and search expressions before they go into your code.
Enter a pattern to begin testing.
How to use the Regex Tester
- Type your regular expression in the pattern box and add flags such as g, i or m.
- Paste your test text below — matches are highlighted live as you type, with a total count.
- Use Copy Pattern to copy the regex with flags, or Clear to reset everything.
Regex Tester — FAQs
Is the regex tester free?
Yes, completely free with no signup and no limits. Test as many patterns as you like, any time, directly in your browser, which is ideal for the iterative trial-and-error style of regular expression development work.
What do the flags mean?
Common flags are g (find all matches, not just the first), i (case-insensitive), m (multi-line, so ^ and $ match line boundaries), s (dot matches newlines) and u (Unicode mode). Any invalid flag characters are stripped automatically.
What happens if my pattern is invalid?
The tool catches the error safely and shows the browser's error message in plain language, such as an unterminated group or a bad quantifier. Fix the highlighted issue and testing resumes live — nothing crashes.
Is my test text uploaded anywhere?
No. All matching runs locally in your browser using the native RegExp engine, so your patterns and test data never leave your device. Nothing is uploaded to a server, logged, or stored anywhere at all.