Regex Tester
Test regular expressions with real-time match highlighting.
What Is a Regular Expression Tester?
A regex tester lets you write a regular expression pattern, apply it to sample text, and see matches highlighted in real time. This is invaluable for developing, debugging, and testing regex patterns before using them in your code. The tool shows all matches, capture groups, and match positions.
How Do I Test a Regex Pattern Online?
Enter your regular expression in the pattern field and paste your test text in the input area below. Matches are highlighted instantly as you type. Toggle flags like global (g), case-insensitive (i), and multiline (m) to modify matching behavior. The tool shows each match with its index position and captured groups.
What Are Common Regex Use Cases?
Regular expressions are used for email validation, phone number formatting, extracting data from log files, search-and-replace operations, URL parsing, input sanitization, web scraping, and data transformation. They appear in virtually every programming language and many text editors.
Why Use an Online Regex Tester Instead of My IDE?
Online testers provide instant visual feedback with syntax highlighting, which is faster than running code and checking console output. They are also useful for sharing patterns with teammates, testing patterns from Stack Overflow answers, and learning regex through experimentation without setting up a project.
What Are the Most Useful Regex Patterns to Know?
Essential patterns include email validation (a simplified version: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}), US phone numbers (\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}), URLs (https?://[\w.-]+(?:\.[\w]{2,})(?:/[\w.-]*)*), and IP addresses (\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}). Test these patterns in the tool above to see them in action.
What Do Regex Flags Like g, i, and m Mean?
The global flag (g) finds all matches instead of stopping at the first. Case-insensitive (i) matches regardless of letter case. Multiline (m) makes ^ and $ match the start and end of each line rather than the entire string. Dotall (s) makes the dot character match newlines. Combine flags as needed — gi is the most common combination for search-and-replace operations.