Regex Tester
Test regular expressions with live match highlighting.
How to Use Regex Tester
- 1Enter your regular expression pattern in the pattern field.
- 2Select the flags you need: g (global), i (case-insensitive), m (multiline), s (dotAll).
- 3Paste or type your test string in the right panel.
- 4Matches are highlighted in real time — view the match list below for positions and values.
Frequently Asked Questions
What regex flavour is used?
JavaScript's built-in RegExp engine — the same one used in Node.js and all modern browsers.
Why are some patterns marked invalid?
If your pattern has a syntax error (unmatched brackets, invalid escape sequences, etc.) the tester shows the error message from the JS engine instead of matches.
Can I test multiline patterns?
Yes — enable the 'm' flag so ^ and $ match line boundaries, and 's' (dotAll) if you need . to match newlines.
About Regex Tester
Regular expressions are one of the most powerful — and tricky — tools in a developer's toolkit. Our Regex Tester gives you a live environment to build, test, and debug patterns without switching between browser consoles or external tools.
As you type, the pattern is compiled in real time and applied to your test string. Every match is highlighted inline and listed below with its value and character index. Invalid patterns display the engine's error message immediately, so you know exactly what to fix.