Regex Tester

How to Use the Regex Tester

This free online regex tester helps you write, test, and debug regular expressions in real time. Simply type your pattern in the input field, choose your flags (global, case-insensitive, multiline), and enter a test string below. Matches are instantly highlighted in the results area, and captured groups are displayed in a structured table so you can inspect every part of your expression.

Regular expressions (regex or regexp) are powerful pattern-matching sequences used across virtually every programming language. They allow you to search, match, extract, and manipulate text based on patterns rather than exact strings. Whether you are validating email addresses, parsing log files, scraping web data, or performing search-and-replace operations, regex is an essential skill for any developer.

Understanding Regex Flags

Flags modify how the regex engine processes your pattern. The global (g) flag tells the engine to find all matches in the string rather than stopping after the first match. The case-insensitive (i) flag makes the pattern match regardless of letter case, so /hello/i matches "Hello", "HELLO", and "hello". The multiline (m) flag changes the behavior of ^ and $ anchors so they match the start and end of each line, not just the entire string.

Common Regex Patterns

• Email: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
• URL: https?:\/\/[^\s]+
• IP Address: \b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b
• Phone Number: \+?\d{1,3}[-.\s]?\(?\d{1,4}\)?[-.\s]?\d{1,4}[-.\s]?\d{1,9}
• HTML Tags: <([a-z]+)([^<]*)(?:>(.*?)<\/\1>|\/>)

Use Cases for Regular Expressions

Developers use regular expressions for a wide range of tasks: form validation (checking if user input matches expected patterns like emails, phone numbers, or postal codes), log parsing (extracting timestamps, error codes, or IP addresses from server logs), data cleaning (removing unwanted characters or normalizing formats), web scraping (pulling structured data from HTML content), and search-and-replace operations in code editors and build tools. Regex is supported natively in JavaScript, Python, Java, C#, PHP, Ruby, Go, and most other modern languages.

This tool runs entirely in your browser using JavaScript's built-in RegExp engine. Your data is never transmitted to any server, making it completely safe for testing patterns against sensitive data. Bookmark this page for quick access whenever you need to build or debug a regular expression.