Regular expression (regex) tester
Write a regular expression, toggle the flags and run it against your text: it highlights matches live and breaks down the capture groups. It uses your own browser's regex engine (JavaScript) and everything happens on your device. The analysis runs in the background with a time limit to protect you from catastrophic patterns.
How to test a regular expression
- Type your regular expression in the pattern field (without the / slashes).
- Toggle the flags you need (global, ignore case, multiline…).
- Paste the test text: matches are highlighted instantly.
- Review the list of matches with their capture groups, both numbered and named.
Frequently asked questions
Which regular expression engine does it use?
The JavaScript (ECMAScript) one, the same as your browser. The syntax is that of JS RegExp objects, which differs in some details from PCRE, Python or .NET.
What do the flags mean?
g (global: all matches), i (ignore case), m (multiline: ^ and $ apply to each line), s (dotAll: the dot also includes line breaks), u (Unicode mode) and y (sticky: anchors the search at the last position).
Does it support named groups?
Yes. Named groups using the (?<name>…) syntax are shown alongside the numbered groups of each match.
What happens if my expression is very slow?
The analysis runs in a separate thread (Web Worker) with a time limit. If your pattern causes catastrophic backtracking (ReDoS) and takes too long, we cancel it and let you know so you can simplify it, without freezing the page.
Is my text or pattern uploaded to a server?
No. All processing happens in your browser; neither the pattern nor the text leaves your device.
Is there any limit?
To keep everything smooth we analyze up to about 50,000 characters of text and show up to 1,000 matches. Enough for the vast majority of cases.