Regex Tester

The Regex Tester is a free regex tester and pattern test tool for building and debugging regular expressions against real sample text, with every match highlighted live as you type. Type a pattern, choose your flags (global, case-insensitive, multiline and more), and see instantly which parts of your text match, along with each capture group broken out separately.

Regular expressions are one of the most powerful — and most commonly misused — tools in a developer's kit. A pattern that looks right can silently match too much, too little, or nothing at all, and debugging that by adding console.log statements inside application code is slow. Testing interactively instead shows you exactly what a regular expression matches in real sample text: log lines you're trying to parse, form input you're trying to validate, a CSV column you're trying to extract, or a URL you're trying to route. It also makes learning regex faster: instead of memorizing what a lookahead or a non-capturing group does in the abstract, you can change one token at a time and watch the highlighted matches update immediately, building intuition through direct feedback rather than documentation alone.

The tester runs on JavaScript's native RegExp engine — the exact same engine used by Node.js and every modern browser — so results here are guaranteed to match what your code will actually do, unlike testers built on a different regex flavor (PCRE, .NET, Python re) that can behave subtly differently around lookbehind, named groups or Unicode property escapes. Invalid patterns surface the browser's own SyntaxError message, pointing at the real problem instead of a generic 'invalid regex'.

Everything runs client-side, so sample text — even if it contains real log data or user records — never leaves your browser.