What is a regular expression?

A regular expression (regex) is a pattern used to match character combinations in strings. It's widely used for search, validation, and text processing in programming.

What do the flags mean?

g (global): find all matches. i (case-insensitive): ignore case. m (multiline): ^ and $ match line boundaries. s (dotAll): . matches newlines. u (unicode): enable Unicode support.

How do capture groups work?

Capture groups are defined with parentheses (). For example, (\d+)-(\d+) captures two groups of digits. Our tool shows all captured groups for each match.

What regex syntax is supported?

Our tester uses JavaScript's built-in RegExp engine, supporting all standard regex features including lookahead, lookbehind, named groups, and Unicode properties.

Yes! All regex processing happens in your browser. No data is sent to any server.

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Regex Tester

Test regular expressions with real-time matching and group highlighting

Your files never leave your browser

Regular Expression

//g

Test String

What is Regex Tester?

Regex Tester lets you write and test regular expressions against sample text with real-time matching and capture group highlighting. It uses JavaScript's native RegExp engine and runs entirely in your browser, so your data stays private.

Key Features

Real-Time Matching

Matches are highlighted instantly as you type your pattern and test string. No need to click a button -- results update live.

Capture Group Details

View all matched groups, including named groups, with their positions and values displayed for each match found.

Flag Support

Toggle regex flags including global (g), case-insensitive (i), multiline (m), dotAll (s), and Unicode (u) to fine-tune matching behavior.

Common Use Cases

Build and validate email, phone number, or URL patterns before using them in production code. Debug existing regex patterns by testing them against real data to understand why matches fail. Learn regular expression syntax interactively by experimenting with patterns and seeing results in real time.

How It Works

Enter Pattern

Type your regular expression pattern

Add Test String

Enter text to test against your pattern

See Matches

Matching parts are highlighted with group details

Frequently Asked Questions

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Last updated: Feb 27, 2026