Regex Tester Online

What Is This Tool?

A regular expression (regex) is a compact pattern language for finding, validating and extracting text: an email pattern can validate form input, \d{4}-\d{2}-\d{2} finds dates, and capture groups pull out the parts you need. Nearly every programming language and editor supports regex.

This tester uses the JavaScript regex engine — the same one that runs in Node.js and every browser — so patterns you build here behave identically in your JavaScript/TypeScript code. Most patterns also work unchanged in Python, Java and Go.

Why Use It?

• Live feedback: matches highlight in yellow as you type the pattern.
• Capture groups shown per match — see exactly what $1 and $2 will contain.
• Full flag support: g (all matches), i (ignore case), m (multiline), s (dot matches newline), u (unicode).
• Clear error messages when the pattern has a syntax mistake.
• Free and private — pattern and text never leave your browser.

How to Use

1. Type your pattern between the two / characters (no need to escape slashes yourself).
2. Adjust flags in the small box after the second / — the default g finds all matches.
3. Paste your test text below.
4. Matches highlight instantly; capture groups are listed underneath.
5. If the pattern is invalid, the error message explains what's wrong.

Example

Input

Pattern: (\w+)@(\w+)\.com
Test string: Contact alice@example.com or bob@test.com

Output

✓ 2 matches
#1 groups: $1=alice  $2=example
#2 groups: $1=bob  $2=test

The parentheses create capture groups you can reference as $1 and $2 in replacements.

Practical tips

• Validating an email input? ^[^\s@]+@[^\s@]+\.[^\s@]+$ is a permissive pattern that catches obvious typos without rejecting valid-but-unusual addresses — full RFC 5322 compliance needs a library, not a one-liner.
• Extracting query params from a URL: [?&]([^=]+)=([^&]*) with the g flag, then read $1/$2 per match instead of hand-splitting on & and =.
• About to use a pattern in .replace()? Test it here first — what highlights is exactly what .replace() will touch, capture groups included.
• Parsing multiline logs (matching a timestamp at the start of each line)? Add the m flag so ^ and $ anchor per line instead of the whole string.
• Copied a pattern from Python or PHP and it doesn't match here? Check for (?P<name>...) named groups — JavaScript uses (?<name>...), no P — or possessive quantifiers (++, *+), which don't exist in JavaScript regex.

A JavaScript regex tester, not a generic one

This tool runs JavaScript's built-in RegExp engine — the exact code path behind str.match(pattern) or pattern.test(str) in a browser console or Node.js. That's different from testing against PCRE (what PHP uses, and what many "universal" regex testers default to) or Python's re module: JavaScript has no possessive quantifiers or atomic groups, and named capture groups use (?<name>...) instead of PCRE/Python's (?P<name>...).

If you're about to ship a pattern inside JS or TypeScript — form validation, a route matcher, a log parser — testing it here means zero flavor mismatch: what highlights on this page is exactly what new RegExp(pattern, flags) matches at runtime.

Where this fits in real workflows

A regex test rarely stands alone. The usual sequence: confirm the pattern here, run the actual .replace() in your code, then diff the before/after text to make sure the substitution did what you expected and nothing else.

Extracting structured data with capture groups often feeds straight into JSON — format the extracted output to check it parsed the way you expected.

→ Text Diff · JSON Formatter

Frequently Asked Questions