JavaScript Regex Tester with Capture Groups

What is a regex tester?

A regex tester lets you write a regular expression and see immediately what it matches against a sample string — every match is highlighted in place and listed with its index and capture groups, updating on each keystroke. That instant feedback loop is the difference between confidently shipping a pattern and discovering in production that it matched too much or too little.

This tester uses JavaScript's native RegExp engine, so what matches here is exactly what will match in Node.js and the browser. Your pattern and test string never leave your machine.

When to use it

Use it while writing validation (emails, slugs, version strings), extracting values from logs or scraped text, building search-and-replace expressions for your editor, or debugging a pattern that behaves differently than you expect. The flag toggles cover the four you'll reach for most: g finds all matches instead of just the first, i ignores case, m makes ^ and $ match at line boundaries, and s lets . match newlines.

Capture groups are shown separately for each match, which makes it easy to check that your parentheses are grabbing the piece you actually want — the most common source of off-by-one regex bugs.

Example

To pull semantic versions out of a changelog, try the pattern (\d+)\.(\d+)\.(\d+) with flags gi against a few lines of release notes. Each match lists three groups — major, minor, patch. When it works, use "Copy link to this result" to share the pattern with your test string embedded in the URL, so a teammate opens exactly what you're looking at.