What Is a Regex Tester? A Regex Tester is a tool that helps you write, test, and debug regular expressions by showing you in real-time whether your pattern matches text correctly. Regular expressions (regex) are special patterns used to search for, match, and manipulate text. The tester provides immediate visual feedback—highlighting matches, showing errors, and explaining what your pattern does. Think of a Regex Tester as a practice sandbox for pattern matching. Instead of writing a regex blind and hoping it works in your actual code, you test it interactively. You enter your regex pattern, provide sample text, and instantly see what matches, what doesn't, and why. For example, if you need to validate email addresses, you write a regex pattern in the tester, paste several example emails (valid and invalid), and immediately see which ones match correctly. This instant feedback prevents hours of debugging later. Why Regex Testers Exist: The Problem They Solve Regular expressions ...