Regex Tester

A regular expression is a compact pattern language for matching text — everything from "does this look like an email address" to "find every phone number in this document" to "strip HTML tags from this string." The catch is that regex syntax is notoriously easy to get subtly wrong: a `.` that should be escaped, a greedy `*` that swallows more than intended, a group that isn't capturing what you expect. Writing one blind and only finding out it's wrong once it's already running against production data is a bad way to learn that lesson.

This tool runs entirely on JavaScript's own built-in `RegExp` engine, executing directly in your browser the moment you type — there's no server involved, so whatever text you're testing against (which might be real user data, log lines, or anything else you'd rather not paste into a third-party service) never leaves your machine. Because it's the exact same engine your JavaScript code will run in production, what you see here — which characters match, how greedy quantifiers behave, whether a group captured anything — is exactly what you'll get at runtime, not an approximation from a different regex flavor.

Type a pattern and flip on the flags you need: `g` to find every match instead of stopping at the first one, `i` for case-insensitive matching, `m` to make `^` and `$` match the start/end of each line rather than the whole string, `s` to let `.` match newlines too. Every match in your test string is highlighted live, and each one is broken down below into its full matched text, its position, and any capture groups — including named groups like `(?<year>\d{4})` — so you can immediately see whether the group you meant to extract is actually the one that matched. The Replace section shows exactly what `String.replace()` would produce with your pattern and a replacement string, including group backreferences like `$1` or `$<year>`.

The quick-reference panel below covers the tokens people forget most often mid-task — the difference between `*` and `+`, what a non-capturing group `(?:...)` is for, how `\b` marks a word boundary — without needing to leave the page to look them up. Once you've got a pattern that behaves the way you want against realistic test data, it's ready to drop straight into your code. If you need to validate or reformat the surrounding data itself, the JSON Formatter & Validator and Text Diff Checker tools are natural companions.