Gemma Gem is a Chrome extension that executes Google’s Gemma 4 model entirely on-device using WebGPU, requiring no API keys or cloud connectivity. The extension hosts the model in an offscreen document that runs an agent loop, exposing tools for reading page content, taking screenshots, clicking elements, typing text, scrolling, and executing JavaScript. A service worker routes messages between content scripts and the offscreen document, enabling the assistant to autonomously browse and interact with any website.