Building Chrome Extensions in 2026: A Practical Guide with Manifest V3

Chrome extensions remain one of the most accessible ways to ship useful developer tools. With Manifest V3 now fully enforced, here's a practical guide to building extensions the right way in 2026. Why Manifest V3? Manifest V3 replaced the old V2 format with a focus on security, privacy, and performance. The key changes include: Service workers instead of persistent background pages Declarative net request instead of webRequest blocking Tighter permissions with explicit host permissions If you're starting a new extension today, V3 is the only option. Project Structure A typical Manifest V3 extension looks like this: my-extension/ ├── manifest.json ├── background.js # Service worker ├── content.js # Content script ├── popup/ │ ├── popup.html │ └── popup.js ├── options/ │ ├── options.html │ └── options.js └── icons/ ├── icon-16.png ├── icon-48.png └── icon-128.png The Manifest File Here's a minimal but complete manifest.json : { "manifest_version" : 3 , "name" : "My Developer Tool" , "ver