Regex Tester
Write a regular expression and see matches, groups and replacements live.
Replace with
Runs 100% in your browser. Your files are not uploaded to any server.
How to use Regex Tester
- Type your pattern and choose flags (g, i, m, s, u).
- Paste or type test text — matches are highlighted as you type.
- Check each match and its capture groups below.
- Enter a replacement like “$2: $1” to preview the result of replace().
Frequently asked questions
Which regex flavor is used?
JavaScript (ECMAScript) regular expressions, exactly as your browser runs them, including named groups (?<name>…) and lookbehind.
What happens with a pattern that hangs?
Matching runs in a background worker with a time limit. If a pattern takes too long (catastrophic backtracking), it is stopped and you get a warning.
Is Regex Tester free?
Yes. Regex Tester is free to use with no sign-up and no watermark.
Are my files uploaded to your server?
No. All processing happens locally in your browser using JavaScript and WebAssembly. Your files never leave your device, which also makes it fast and private.
Does it work on my phone?
Yes. It works in any modern browser on Windows, Mac, Linux, Android and iPhone. Very large files may be slow on older phones.