Mac App Store

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To download Duo from the Mac App Store, you need a Mac with OS X 10.6.6 or later. Learn More.


By Electric Pulp

Open the Mac App Store to buy and download apps.


Duo is a dual-paned web browser built for Responsive Web Design (RWD) that lets you browse the web in two views: your standard ‘desktop’ view as well as a typical ‘mobile’ view. By seeing these two views at the same time, you’re able to quickly test and work through multiple screen experiences rather than considering them separately.

Whether you’re a designer or a developer, project manager or client, Duo gives you a new tool to make your Responsive Web Design project go more smoothly than ever.

Get the bookmarklet:

Duo gives you an adjustable mobile view using the left pane.

The right pane defaults to an adjustable tablet / desktop view.

Navigating in either pane updates the other. No need to reload layouts to view pages at different sizes.

Duo has everything you need to make sure your design is doing what it should. Debug code in either pane.

Duo includes tools for clearing your cache and getting rid of those pesky cookies via standard key commands.

• LiveReload SUPPORT
Duo now includes support for LiveReload.

Use the convenient bookmarklet in your other browsers to push a site over to Duo. Get the bookmarklet:


Duo is designed for Responsive Web Design, not for user-agent sniffing. Duo also only refreshes both views for GET requests. It's probably not a good fit for your POST refresh heavy project, although we are actively looking at ways to accommodate this.

You can email for support, or reach out to us on Twitter: @electricpulp. Thanks!

What's New in Version 1.3

LiveReload Support


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Customer Reviews

Almost there ...

I love the simple user interface. And this really helps when previewing fully responsive sites; but if also let you set the user agent … that would make it complete, to me.

Still working in Sierra

Lightweight brwoser for protyping two screen sizes at once. Works with LiverReload and Browsersync. One unfortunate rendering problem caused me some grief. There is an issue with `border-radius` rendering. You’ll see a small gap between the `border` and the `background-color`. This is a bug not work chasing, so do not expect to use Duo as a QA tool. This is merely a quick prototyping tool. It’s unfortunate that it’s not maintained as it’s being taken over by the Chrome plug-in, Pointbreak.

Not real mobile view, very limited options...

Just purchased and tried, here is what I found wrong:

1. The mobile view gives you a “frame” of your website, and not the “real view” of it on a real mobile device. In other words, on my mobile phone I can see my complete website page, reduced in size of course, fitting the full screen, whereas on this program I can see just a portion of the screen without size reduction which is not the real view you get on a mobile device.

2. There is no way to access any settings to target specific screen devices. I really expected that!

For me, this app is useless and deceptive. To test my website for repsonsive design, I am going to use a real device.

View in Mac App Store
  • $4.99
  • Category: Developer Tools
  • Updated:
  • Version: 1.3
  • Size: 1.7 MB
  • Language: English
  • Seller:

Compatibility: OS X 10.8 or later, 64-bit processor

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