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TOOL · 58 · Data & Utility

Regex Tester

Test JavaScript regular expressions live — highlighted matches, capture groups and replacement preview.

In short
Regex Tester lets you build and debug JavaScript regular expressions live — highlighted matches, capture groups, all six flags and a replacement preview using $1/$2 backreferences.

Processed 100% in your browser — your files never leave your device.

Highlighted

Contact Alice at alice@example.com or Bob at bob@site.co.

2 matches

  1. #1 alice@example.comgroups: $1="alice", $2="example.com"
  2. #2 bob@site.cogroups: $1="bob", $2="site.co"

How it works

  1. Step · 01

    Write a JavaScript regular expression pattern and toggle the flags you want.

  2. Step · 02

    Matches highlight live in the sample text; capture groups appear in the match list.

  3. Step · 03

    Optionally provide a replacement string (supports $1, $2 backreferences).

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Frequently asked questions

Which regex dialect is this?
JavaScript / ECMAScript regex (RegExp). Most PCRE features work; look-behinds, named groups and unicode escapes are supported in modern browsers.
Why do I get 'Nothing to repeat' or a similar error?
Your pattern isn't valid JS regex — usually an unescaped special character. Fix the pattern and matches will re-run automatically.
Are my files uploaded to a server?
No. Files are processed directly in your browser using JavaScript and WebAssembly. Nothing is uploaded to our servers, so your documents never leave your device.
Does it work on mobile?
Yes. The tools run in any modern browser on desktop, tablet, or mobile (Chrome, Edge, Safari, Firefox). Very large files may be slower on low-end phones.