Free Regex Tester Online

Regex Tester is a live regular expression playground that highlights all matches in your test string as you type. Regular expressions (regex) are a powerful pattern-matching language used across programming to validate input, extract data, and transform text. Writing regex by hand can be error-prone — a small mistake can cause unexpected matches or catastrophic backtracking. This tool shows matches in real time, making it easy to iterate and debug patterns quickly.

The tester uses JavaScript's RegExp engine. As you type, the pattern is compiled and executed against your test string. Each match is highlighted with its index position and captured groups displayed. Named groups (?<name>...) are also extracted and shown. A 1000-match cap prevents runaway matches from freezing the browser.