Tools / Regex Tester
Regex Tester
Test JavaScript regular expressions against sample text with live highlighting and capture groups — entirely in your browser.
JavaScript flavor (RegExp). 4 matches
The@0Contact@45Invoice@100Server@139
// About this tool
Regex Tester
This regex tester runs JavaScript regular expressions against sample text with live match highlighting. Type a pattern, toggle the flags (global, case-insensitive, multiline, dotall, unicode), and see every match with its position and capture groups instantly.
The tool uses the standard JavaScript RegExp engine — the same one in Node.js and every modern browser — with a clear 'JavaScript flavor' note, because regex dialects differ across languages.
Everything runs locally in your browser. Your patterns and test text are never uploaded, which makes it safe for working with data you cannot paste into an online service.
// When to use it
Build a pattern iteratively
Watch matches update live as you refine a pattern, instead of round-tripping through a terminal or docs.
Debug capture groups
Each match lists its capture groups ($1, $2, …) so you can see exactly what your parentheses are capturing.
Verify a pattern against real data
Paste a sample of production-style data (emails, IPs, log lines) and confirm the pattern matches what you expect.
// Questions
Is my pattern or text uploaded?
No. All matching happens locally in your browser using the standard JavaScript RegExp engine. Nothing is sent to a server.
Which regex flavor does this use?
JavaScript (ECMAScript). That is the same engine used by Node.js and modern browsers, but it differs from PCRE, Python, or Go regex in some syntax details.
Does it support lookahead and lookbehind?
Yes. JavaScript supports lookaheads, and modern engines support lookbehinds. If your pattern uses unsupported syntax, you will get an error message instead of silent misbehavior.
Why does my global match show nothing?
Some patterns match zero-length strings or require the g flag to find all occurrences. Try toggling the g flag, or check the error line under the pattern input.
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