Sizzy

About

Sizzy is a desktop browser for web developers, built on Chromium so pages look the way they will for your users. It puts every device side by side in one window, with isolated sessions, debugging tools, terminals, and coding agents alongside the page you are testing. The site lists it for macOS, Windows, and Linux.

Devices move together on one canvas. You pick real device sizes with real viewports and user agents, and scrolling, clicks, typing, and navigation stay in sync across them until you turn sync off. Sessions are isolated browser profiles with their own cookies, cache, and local storage, so you can assign a different session to each device and test what an admin, a customer, and a guest each see at the same time.

Each project keeps its URLs, devices, sessions, notes, snippets, and terminals, and remembers the repo path, dev command, and package manager. A debugging panel provides a console, docked Chromium DevTools, storage and CSS editors, request headers, and an API client. You can also run your dev command, open terminals, and hand tasks to Claude Code or Codex without leaving the page you are testing.