What is a regular expression (regex)?

A regular expression is a concise pattern used to match, search, and manipulate strings. It’s widely used for validation, parsing, and find/replace tasks.

How do I test a regex with this tool?

Enter your pattern in the regex input, choose flags like g, i, or m, then paste sample text. Matches and capture groups update in real time.

Which regex engine does this tool use?

This tool evaluates patterns using your browser’s JavaScript RegExp engine, which follows the ECMAScript specification.

Can I preview replacements?

Yes. Provide a replacement string and the tool shows a live preview of the result, including support for numbered capture groups like $1, $2.

Do you support multiline and case-insensitive matching?

Yes. Toggle m for multiline, i for case-insensitive, and g for global matching to control how the pattern is applied.

Is the Regex Tester free to use?

Yes. It’s completely free and runs in your browser—no login or installation required.

Regex Tester & Pattern Validator

You need to enable JavaScript to use this tool.

Test regular expressions online with instant feedback. Paste your pattern, toggle flags (g, i, m), provide sample text, and view matches, groups, and replacements.

Features:

Live Matching – Real-time highlight of matches and capture groups
Flags – Global, case-insensitive, and multiline support
Replace Preview – See output using $1, $2… placeholders
Indices – Start/end positions for each match
Cheatsheet – Quick reference for tokens and character classes
Free & Private – Runs in your browser