Regex tester
Test regular expressions live with match highlighting, capture groups and flags.
Regular expression in JavaScript syntax without surrounding slashes, for example [0-9]{5} for a five-digit postcode. Toggle the flags g, i, m, s and u with the buttons next to it.
The text to search in. Matches are highlighted below; everything runs only in your browser.
How this tool works
The regex tester lets you test regular expressions directly in your browser with live highlighting of all matches, capture groups and named groups. All JavaScript flags (g, i, m, s, u) are supported. No server transfer — safe for sensitive input like log lines or personal data.
Typical use cases
- Test email validation regex before deployment
- Develop log parsing patterns and visually inspect matches
- Debug named capture groups for URL routers
- Split CSV/TSV lines with regex and inspect groups
Frequently asked questions
Are my inputs sent to a server?
No. The regex tester runs entirely in your browser. No network request, no storage.
Which regex syntax is supported?
JavaScript/ECMAScript syntax including lookbehind, named groups, unicode properties (with u flag) and dotAll (s flag).
What happens with an invalid pattern?
The browser raises a SyntaxError. The error message is displayed directly so you can fix the pattern.
How do I enable multiline mode?
Click the m flag button. Then ^ and $ match line start/end instead of just string start/end.
Is there an input length limit?
No hard limit — with very large strings (>1 MB) highlighting may become slow since it runs in the UI thread.
Does the tool support PCRE syntax?
No — it uses the JavaScript RegExp engine. PCRE features like recursive patterns, conditionals or possessive quantifiers are not available.
Related tools
Continuous monitoring vs. one-shot?
XICTRAQ monitors uptime, SSL, security headers, GDPR and performance 24/7. Free plan, no credit card.