Question 1

How do I test a regular expression online?

Accepted Answer

Enter your regex pattern and the test text into our Regex Tester. Matches are found instantly in your browser using the JavaScript RegExp engine, with no data ever leaving your device.

Question 2

What regex flags are supported?

Accepted Answer

Our tester supports all standard JavaScript regex flags: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode), v (unicodeSets), y (sticky), and d (indices). Invalid flags are removed automatically.

Question 3

Can I use capture groups in the regex tester?

Accepted Answer

Yes. The tester uses JavaScript's RegExp.exec() method, which supports capture groups, named groups, and lookaheads. All matches including group captures are returned for each match found.

Question 4

Why does my regex cause an infinite loop?

Accepted Answer

A zero-length match inside a global regex loop can cause infinite iteration. Our tester automatically advances lastIndex when a zero-length match is detected, preventing hangs in the browser.

Regex Tester | Free Online Regular Expression Checker

Test Text

Matches: 2

Online regex tester tool

Test Text

Matches: 2