Regex Tester
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What is a Regex Tester?

A regular expression (regex) is a powerful pattern matching language used to find, validate, extract, or replace specific patterns in strings. It is essential in programming, data analysis, text processing, and many other fields.

This online regex tester allows you to enter a regular expression and instantly see matching results in real-time. It supports capture group analysis, string replacement, and various flag settings. Test your patterns directly in your web browser without any complex development environment.

Key Features

Real-time Matching

Enter your regex and test string to instantly see highlighted matching results.

Capture Group Analysis

View detailed capture groups, index positions, and matched values for each match.

Replace Functionality

Instantly see the result of replacing matched patterns with your desired string.

Preset Patterns

Apply commonly used regex patterns for email, phone, URL, IP, Korean characters with one click.

How to Use

  1. Enter Regex — Type your regular expression pattern in the input field at the top.
  2. Set Flags — Enable flags like g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode) as needed.
  3. Enter Test String — Type the string you want to test against and see real-time matching results.
  4. Check Results — Review match highlights, capture group details, and replacement results.

Use Cases

Input Validation

Validate email, phone number, and password formats in registration forms using regex.

Log Analysis

Extract specific patterns like IP addresses, error codes, and timestamps from server logs.

Data Cleaning

Remove unwanted characters or convert formats in CSV and text data.

Code Refactoring

Use regex in your IDE's find/replace to batch-modify code patterns.

FAQ

What is a regular expression?

A regular expression (regex) is a formal language for defining and searching patterns in strings. It is supported by most programming languages and text editors, and is used for data validation, extraction, and replacement.

What are flags and what types are available?

Flags modify how a regex behaves. Common flags include g (global search), i (case-insensitive), m (multiline mode), s (dotAll - dot matches newline), and u (unicode support).

What are capture groups?

Capture groups are parts of a regex enclosed in parentheses (). They allow you to extract specific portions of matched strings and reference them as $1, $2, etc. during replacement.

Is this tool free?

Yes, it is completely free with no registration or installation required. Your input data is never sent to any server.

What regex syntax is supported?

This tool uses JavaScript's (ECMAScript) regex engine. It supports most standard regex syntax including character classes, quantifiers, anchors, lookahead/lookbehind, and more.

Privacy Notice

This regex tester performs all processing in your browser. Your regular expressions and test strings are never sent to any server. You can safely test sensitive data.