What is a regex tester used for?

A regex tester helps developers validate regular expressions before using them in code. It provides real-time matching feedback, shows capture groups, and helps debug pattern matching logic for email validation, URL extraction, and other text processing tasks.

What are regex flags?

Regex flags modify how the pattern matching works. Global (g) finds all matches, case-insensitive (i) ignores letter case, multiline (m) treats line breaks as boundaries, and dotall (s) makes dot match newlines.

How do I test a regex pattern?

Enter your regex pattern in the pattern field, select desired flags, and type or paste text to test in the test string field. The tester shows all matches in real-time with match count and position information.

What are capture groups in regex?

Capture groups are parts of a regex pattern enclosed in parentheses. They allow you to extract specific portions of matched text. For example, in email validation, capture groups can extract the username and domain separately.

Regex Tester & Debugger — Free Pattern Testing Tool

About Regex Tester & Debugger

Our free online regex tester and debugger helps developers test, validate, and refine regular expression patterns with real-time feedback. Whether you're validating email addresses, extracting phone numbers, or building complex pattern matching logic, this tool provides instant visual feedback to debug your regex quickly and efficiently.

What is Regular Expression?

A regular expression (regex or regexp) is a sequence of characters that defines a search pattern. It's a powerful tool used in programming and text processing to match, validate, and extract specific text patterns. Regular expressions are used for email validation, phone number extraction, URL parsing, data validation, and countless other text processing tasks.

Key Features

Real-Time Testing: See matches as you type your regex pattern
Regex Flags Support: Use global (g), case-insensitive (i), multiline (m), and dotall (s) flags
Capture Groups: View captured groups from your regex matches
Match Highlighting: Visual highlighting of all matches in test string
Quick Patterns: Pre-built regex patterns for email, URL, phone, IP address, and more
Match Statistics: Count total matches and find first match position
Copy Results: Easy copying of matched results
Error Detection: Clear error messages for invalid regex patterns

Understanding Regex Flags

Global (g): Matches all occurrences of the pattern, not just the first one. Case-Insensitive (i): Makes the pattern match both uppercase and lowercase letters. Multiline (m): Treats the beginning and end anchors (^ and $) as line boundaries, not just string boundaries. Dotall (s): Makes the dot (.) match newline characters as well as all other characters.

Common Regex Patterns for Validation

Email validation, phone number formatting, URL extraction, and IP address validation are among the most common regex use cases. This regex tester includes quick-insert buttons for these popular patterns so you can test immediately without needing to memorize the exact syntax. Each pattern is optimized to handle the most common formats while remaining flexible enough for variations.

Testing Regex Patterns Online

Our online regex tester makes it easy to validate your patterns before using them in production code. The real-time matching feature shows you exactly what your pattern will match, helping you catch edge cases and unexpected results. This prevents bugs in your code by allowing you to test thoroughly before implementation. The visual feedback makes it simple to refine patterns until they work exactly as intended.

Debugging Regex Errors

When your regex doesn't work as expected, our debugger provides clear error messages and match statistics to help identify the problem. The capture groups display shows exactly what each part of your pattern is capturing, making it easy to diagnose issues with complex expressions. Test different variations of your pattern and see the results instantly.

Regex Tester & Debugger

Quick Patterns

Related Tools

JSON Formatter

Diff Checker

Slug Generator

Hash Generator