Is the regex tester free?

Yes, completely free. No account, no limits.

What regex flavor does it support?

The tester uses JavaScript's built-in RegExp engine. This is compatible with Node.js, browser JavaScript, and most modern languages with minor syntax differences.

Can I test capture groups?

Yes. Capture groups are displayed with their matched values alongside the full match details.

Regex Tester - Test & Debug Regular Expressions Free Online