Regex Tester Online Tutorial: Learn Regular Expressions From Scratch

Regex Tester Online Tutorial: Learn Regular Expressions From Scratch Regular expressions (regex) look intimidating. A pattern like ^(?=.*[A-Z])(?=.*\d).{8,}$ looks like noise until you understand the parts. Once you do, regex becomes one of the most useful tools in a developer's toolkit — for validation, parsing, search-and-replace, and data extraction. This tutorial teaches regex from the ground up, using a live online tester so you can experiment as you learn. Where to Practice Open DevPlaybook Regex Tester in another tab. As you read each section, type the patterns and test them against the examples. Regex is learned by doing. The AI Regex Explainer is also useful — paste any complex regex and get a plain-English explanation of what each part does. Part 1: The Basics Literal Characters The simplest regex is just text. The pattern cat matches the string "cat" anywhere it appears: Test string Match? cat ✅ matches "cat" concatenate ✅ matches "cat" inside "concatenate" CAT ❌ case-sensit