What is a regular expression?

A regular expression (regex) is a sequence of characters that defines a search pattern. Regex can match specific strings, validate formats (email, phone), extract data, and perform find-and-replace operations in text.

What regex engine does this tool use?

This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript regex specification. It's compatible with patterns used in JavaScript, TypeScript, and most modern programming languages.

What are regex flags?

Flags modify how the pattern matches: g (global) — find all matches; i (case insensitive) — match regardless of case; m (multiline) — ^ and $ match line start/end; s (dotAll) — dot matches newlines; u (unicode) — full Unicode support.

How do I match an email address with regex?

A simple email regex: /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/. Note that a truly comprehensive email regex is extremely complex — for production, use an email validation library.

What are capture groups?

Parentheses () create capture groups that extract specific parts of a match. (?:...) is a non-capturing group. Named groups (? ...) let you reference captures by name instead of number.

Regex Tester - Test Regular Expressions Online Free | ToolsArena

How to Use Regex Tester

1
Enter your regular expression pattern in the "Regex" field.
2
Toggle flags (g, i, m, s, u) using the flag buttons.
3
Enter or paste your test string in the "Test String" area.
4
Matches are highlighted in real time with different colors for each match.
5
See all match details, capture groups, and indices in the results panel.

About Regex Tester

Regular expressions (regex) are powerful pattern-matching tools used in virtually every programming language for string searching, validation, and text processing. Our Regex Tester provides a real-time environment to write, test, and debug regex patterns with instant visual feedback — matching text is highlighted in color as you type.

The tester shows all matches, capture groups, and group values clearly. You can enable flags (global, case insensitive, multiline, dotAll, sticky, unicode) with simple toggles. The tool also shows your regex pattern's structure breakdown, helping you understand what each part does.

Common use cases: validating email addresses, phone numbers, dates, and URLs; extracting specific data from text; find-and-replace operations; parsing log files; and building form validation in web applications. This is an indispensable tool for developers, data engineers, and QA engineers.

Regex Tester