This is an introduction to developing Chrome Extension for beginners. This includes a fully working sample of the Chrome Extension. Let's make your own Chrome Extension! This book is compatible with Manifest V3 implemented in Chrome 88 released on January 19, 2021. The Manifest V2 is likely to be deprecated in the future, so if you're starting now, we recommend Manifest V3. Index Chapter 1. Very simple chrome extension. Chapter 2. How to use localStorage. Chapter 3. How to Debug. Chapter 4. Browser Action and Page Action. Chapter 5. How to use executeScript. Chapter 6. How to use contextMenus. Chapter 7. Control chrome tabs. Chapter 8. How to use sendMessage. Chapter 9. How to use Alarm. Chapter 10. How to use content scripts. Chapter 11. Open file and Sava to file.