Best Free Online Regex Tester

Writing correct regular expressions is genuinely difficult. The syntax is compact, edge cases are subtle, and the feedback loop of writing a pattern, running code, and checking output is slow. devtoolkit.sh's Regex Tester eliminates that cycle by testing your expression against a live input string as you type, highlighting every match in real time. You can set any combination of JavaScript regex flags — global (g), case-insensitive (i), multiline (m), dotAll (s), and Unicode (u) — and see immediately how they change the matching behaviour. Each match and its captured groups are listed below the input with their start and end positions, making it easy to verify that your regex captures exactly what you intend and nothing more. This tool is invaluable for building patterns for form validation, parsing log files, writing search-and-replace transformations, and understanding how an existing regex in a codebase actually works. Named capture groups are supported and displayed clearly, which is useful for documenting complex patterns intended for team review.