Sizzy

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Introduction

Sizzy describes itself as a desktop browser for web developers: every device side by side, isolated sessions, debugging tools, terminals and coding agents in one window.

It is built on Chromium. Devices stay in sync for scrolling, clicks, typing and navigation, and isolated sessions keep cookies, cache and storage separate, so you can be ‘the admin, the customer and a stranger at the same time’, in the site’s words. Projects keep their URLs, devices, sessions, notes, snippets and terminals together.

For QA, isolated sessions are useful for testing multi-role flows, and synced devices speed up responsive checks.

In the quality loop it supports manual responsive and multi-user checks while building.

Features

1. Synced devices: Real device sizes side by side.
2. Isolated sessions: Separate storage per session.
3. Unified console: One console for all devices.
4. Projects: Keep URLs, devices and notes per project.
5. Terminals and agents: Built-in terminals and coding agents.

Pros

1. Multi-role testing: Several logged-in users at once.

Cons

1. Chromium only: No Safari or Firefox engines.
2. Paid: Subscription or lifetime licence.

Usage and Links (Example)

Download Sizzy, create a project for your app, add devices and sessions for each user role, and test flows side by side.

Resources:

• Sizzy website

Pricing

$15/month, $12/month billed annually ($144/year) or a $499 one-time lifetime licence, per the pricing page. See site.

Recommended for?

1. Developers testing responsive and multi-role flows manually.
2. Not a fit for automated testing.

Conclusion

Sizzy packs responsive previews and multi-session testing into one developer browser.

On CheckOps, Sizzy is filed under the Prototype & UX testing and End-to-end & functional stages. Related tools listed here include Polypane, Responsively App, Browserling, Chromatic, LambdaTest and BrowserStack. Before choosing, compare them on licence, supported languages and platforms, hosting model, and how well each fits your existing CI pipeline. Facts on this page were checked against the official website, documentation and repository on 11 November 2026; statements the vendor makes about its own product are marked as vendor claims.