Regex Tester

Writing a regular expression is often a cycle of guess, test, squint at the result, and adjust — and that cycle is only as fast as your tool lets it be. Many regex testers show you a bare true/false or a match count and leave you to work out which part of your text actually matched. This one highlights every match directly inside your test string as you type, so you see immediately which characters your pattern actually captured, not just whether it captured something.

Capture groups get the same direct treatment. For every match, both numbered groups ($1, $2, and so on) and named groups (?<name>...) are broken out individually with their actual matched values, rather than leaving you to count parentheses by hand or dig through a nested result object. This matters most for exactly the patterns people struggle with — multi-group patterns for parsing dates, URLs, or log lines, where knowing which piece landed in which group is the whole point of the exercise.

Replace mode goes a step further than matching: type a replacement pattern using $1, $2, or $<name> references, and see the actual resulting text live, exactly as JavaScript's own string replace would produce it. This is the difference between confirming a pattern matches and confirming a find-and-replace operation will actually do what you intend — a distinction that matters a lot once you're about to run that same replacement across a real codebase or dataset.

A library of ready-made common patterns — email addresses, URLs, IPv4 addresses, hex colors, US phone numbers, ISO dates — gives you a working, testable starting point with one click, rather than a blank pattern box and a blinking cursor. Every part of this — matching, highlighting, capture-group extraction, replacement preview — runs using your browser's own regular expression engine, entirely on your device.