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Regex Tester

100% Free

Live regex testing with highlighted matches, capture groups, named groups, and JS-engine flag toggles (i/m/s/u/y).

Real-time
Client-Side
JS engine
Highlighted matches 2 matches
Email me at alice@example.com or bob@test.io
Match details
Match 1at index 12
alice@example.com
$1alice
$2example.com
Match 2at index 33
bob@test.io
$1bob
$2test.io

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<iframe
  src="https://tools.town/embed/regex-tester/"
  width="100%"
  height="600"
  style="border:none; border-radius:12px;"
  loading="lazy"
  title="Regex Tester">
</iframe>

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How to Use

  1. 1 Type your regex pattern (without surrounding slashes)
  2. 2 Toggle flags as needed: i, m, s, u, y
  3. 3 Type or paste test text
  4. 4 Matches highlight in yellow, with capture groups listed below

Features

  • Live highlighting of all matches
  • Capture groups numbered ($1, $2, …)
  • Named groups (?<name>…) shown separately
  • All 5 user-toggleable JS flags
  • Always uses 'g' globally — find every match
  • Parse errors surface with the engine's exact message

Why it Matters

Regex is the universal text-processing tool but writing one by trial and error is slow. A live tester with highlighted matches and group breakdowns turns a 30-minute debug into 30 seconds — easier than firing up a Node REPL or a regex testing site that requires an account.

★★★★★

Use Cases

Build a Validator

Iterate on a regex for email/phone/URL validation

Log Scraping

Test a pattern against a sample log line before deploying

Learning Regex

See exactly what each part of your pattern matches

Frequently Asked Questions

Which regex flavour does this use?
JavaScript's native RegExp engine — same behaviour as your browser's. NOT Perl-compatible (PCRE), NOT POSIX. Most patterns are interchangeable but some lookbehind / Unicode features differ.
Why is the 'g' flag forced on?
Without 'g', JavaScript's matchAll throws. We always want every match for a useful tester, so 'g' is implicit.
What does the 'y' (sticky) flag do?
Matches only at the regex's `lastIndex` position — useful for tokenizers but rarely for one-off patterns. Toggle on if you need it.
📖

Want to understand the math?

Browse all guides →
How to Use Regex Tester
regex

How to Use Regex Tester — Complete Guide

Learn how to write, test, and debug regular expressions in real time using Tools.Town's free Regex Tester — with match highlighting and group capture.

8 May 2026

5 min read

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