Gemma Gem

Your personal AI assistant living right inside the browser. Gemma Gem runs Google's Gemma 4 model entirely on-device via WebGPU — no API keys, no cloud, no data leaving your machine. It can read pages, click buttons, fill forms, run JavaScript, and answer questions about any site you visit.

Requirements

• Chrome with WebGPU support
• ~500MB disk for model download (cached after first run)

Setup

pnpm install
pnpm build

Load the extension in chrome://extensions (developer mode) from .output/chrome-mv3-dev/.

Usage

1. Navigate to any page
2. Click the gem icon (bottom-right corner) to open the chat
3. Wait for model to load (progress shown on icon + chat)
4. Ask questions about the page or request actions

Architecture

Offscreen Document          Service Worker           Content Script
(Gemma 4 + Agent Loop)  <-> (Message Router)    <-> (Chat UI + DOM Tools)
       |                         |
  WebGPU inference          Screenshot capture
  Token streaming           JS execution

• Offscreen document: Hosts the model via @huggingface/transformers + WebGPU. Runs the agent loop.
• Service worker: Routes messages between content scripts and offscreen document. Handles take_screenshot and run_javascript.
• Content script: Injects gem icon + shadow DOM chat overlay. Executes DOM tools (read_page_content, click_element, type_text, scroll_page).

Tools

Tool	Description	Runs in
read_page_content	Read text/HTML of the page or a CSS selector	Content script
take_screenshot	Capture visible page as PNG	Service worker
click_element	Click an element by CSS selector	Content script
type_text	Type into an input by CSS selector	Content script
scroll_page	Scroll up/down by pixel amount	Content script
run_javascript	Execute JS in the page context with full DOM access	Service worker

Settings

Click the gear icon in the chat header:

• Thinking: Toggle native Gemma 4 chain-of-thought reasoning
• Max iterations: Cap on tool call loops per request
• Clear context: Reset conversation history for the current page
• Disable on this site: Disable the extension per-hostname (persisted)

Development

pnpm build              # Development build (with logging, source maps)
pnpm build:prod         # Production build (logging silenced, minified)

Tech Stack

• WXT — Chrome extension framework (Vite-based)
• @huggingface/transformers — Browser ML inference
• marked — Markdown rendering in chat
• Gemma 4 E2B (onnx-community/gemma-4-E2B-it-ONNX) — q4f16 quantization, 128K context

Debugging

All logs are prefixed with [Gemma Gem]. In development builds, info/debug/warn logs are active. Production builds only log errors.

• Service worker logs: chrome://extensions → Gemma Gem → "Inspect views: service worker"
• Offscreen document logs: chrome://extensions → Gemma Gem → "Inspect views: offscreen.html"
• Content script logs: Open DevTools on any page → Console
• All extension pages: chrome://inspect#other lists all inspectable extension contexts (service worker, offscreen document, etc.)

The offscreen document logs are the most useful — they show model loading, prompt construction, token counts, raw model output, and tool execution.

Notes

The agent/ directory has zero dependencies. It defines interfaces (ModelBackend, ToolExecutor) and can be extracted to a standalone library.