Regex Tester

What this tool does

This tool runs a regular expression against sample text using your browser's native RegExp engine — the same engine that powers String.prototype.match and .replace in JavaScript — and highlights every match live as you type. Toggle the global, case-insensitive, multiline, and dot-matches-newline flags to see how each one changes what matches. Everything runs locally in your browser.

Example use case

Before dropping a regular expression into validation code, a build script, or a find-and-replace, it's worth confirming it actually matches what you expect — and only what you expect. Pasting a pattern like an email or phone number matcher here against a block of real sample text quickly surfaces both false negatives (things it should match but doesn't) and false positives (things it matches but shouldn't).

Common flags

The global flag finds every match instead of stopping at the first one, which is almost always what you want when testing. Case-insensitive matching ignores letter case. Multiline mode changes ^ and $ to match the start and end of each line rather than the whole string, and dot-matches-newline lets . match line break characters it would otherwise skip.