Features
- Live highlighting of every match as you type.
- A table of matches with their position and capture groups.
- Replace preview using
$1,$2or named groups$<name>. - Flags: g (global), i (ignore case), m (multiline), s (dot matches newline), u (unicode).
- A 2-second safety timeout: patterns with catastrophic backtracking are stopped instead of freezing your browser.
Quick reference
| Token | Matches |
|---|---|
\d / \w / \s | digit / word character / whitespace |
. | any character except newline |
* + ? {2,5} | 0+, 1+, 0–1, 2–5 times |
^ / $ | start / end of line (with m) or text |
(…) / (?:…) | capture group / non-capturing group |
The tester uses the JavaScript regex engine, which matches the behaviour of Node.js and browsers; most patterns also work in PHP (PCRE) and Python.
Frequently asked questions
Which regex flavour is used?
JavaScript (ECMAScript). Syntax is very close to PCRE, but lookbehind support and some flags differ in other languages.
Why was my regex stopped?
It ran for more than 2 seconds, usually because of nested quantifiers like (a+)+ that cause catastrophic backtracking.
Do I include the slashes?
No. Enter only the pattern and choose flags with the checkboxes.