Regex Tester

About Regex Tester

The Regex Tester lets you write, test, and debug regular expressions in real-time. Enter a pattern and test string to instantly see all matches highlighted, capture groups extracted, and match details displayed — an essential tool for developers working with text parsing, input validation, data extraction, or search-and-replace operations across any programming language.

What Are Regular Expressions?

Regular expressions (regex) are powerful pattern-matching sequences used to search, validate, and manipulate text. They are supported by virtually every programming language (JavaScript, Python, Java, C#, PHP, Go, Ruby) and are essential for tasks like form validation, log parsing, data extraction, and text transformation. Despite their power, regex patterns can be difficult to write and debug — this tool provides instant visual feedback so you can see exactly what your pattern matches before using it in production code.

Key Features

• Real-time matching — see matches highlighted instantly as you type the pattern or modify the test string.
• Capture group display — view all numbered and named capture groups for each match with their exact values.
• Flag support — toggle global (g), case-insensitive (i), multiline (m), dotAll (s), and Unicode (u) flags.
• Match details — see match index, length, captured text, and group details for every match found.
• Sample patterns — load pre-built regex patterns for common tasks like email validation, URLs, dates, IPs, and phone numbers.
• Replace mode — test search-and-replace operations with capture group references in the replacement string.

How to Use

1. Enter pattern — type your regular expression in the pattern field (without surrounding slashes).
2. Enter test string — paste or type the text you want to match against.
3. Set flags — toggle regex flags (g for global, i for case-insensitive, m for multiline) as needed.
4. View results — matches are highlighted in the test string with capture group details shown below.

Common Regex Patterns

• Email: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
• URL: https?:\/\/[\w.-]+(?:\.[\w.-]+)+[\w.,@?^=%&:/~+#-]*
• IPv4: \b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b
• Date (YYYY-MM-DD): \d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])
• Phone: \+?\d{1,3}[-.\s]?\(?\d{1,4}\)?[-.\s]?\d{1,4}[-.\s]?\d{1,9}

Real-World Use Cases

• Testing email, URL, phone number, or custom validation patterns before implementing them in application code.
• Debugging complex regex patterns by seeing live highlighted matches in real test data.
• Extracting structured data from log files, CSV rows, or semi-structured text using capture groups.
• Building search-and-replace transformations for batch text processing or code refactoring.
• Learning regular expressions interactively with immediate visual feedback on pattern behavior.