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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

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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.

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 1.1.6

First of all, thanks to everyone who provided input and thoughts on Duo. We're excited about this update. It includes some adjustments based on your input as well as several bug fixes.

Be sure to check out the resizable panes, improved scrolling and customizable tool bar.


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Customer Reviews

Great idea, awaiting more robust implementation

I was so intrigued by this, as a potentially useful tool to add to my responsive design workflow, that I bought it on impulse. I don't necessarily regret it, but there are some features I'd love to see added to make it live up to my hopes.

In its current form, I wonder if having two viewports glued together, with little else, competes with two different browser windows open side by side and loaded with various 3rd party extensions.

- It would be great if there were preset sizes that could be quickly and easily set for each of the two viewports. For example, there are a number of "Resize Browser" extensions on the market that let you select from a drop down of preset sizes (and set custom sizes as well), and it will change the browser window to those dimensions. So, if there were presets like iPad portrait, iPad landscape, Nexus 7 portait etc. iPhone portrait seems to be the default for the mobile size, would be great to get other portrait presets and maybe even landscape too.

- A bandwidth simulator for each viewport would be pretty cool as well, allowing you to preview the mobile side at 3G speed compared to desktop side at Broadband and such

- Being able to export the current side-by-side screen views to a Bitmap (PNG) might also be a handy shortcut to having to screen grab manually

Anyhow, I look forward to possible updates in the future, thanks for your consideration.

Loving this little app!

I’ve been hesitant on using Duo for a month or two, but finally dove in. I can already see it creeping into my work flow and I’ve had it for about 10 minutes. It’s not the end all be all, but for designing with a mobile first strategy it will be a wonderful tool to help in my build process.

Thanks Electric Pulp!

Just $5 for a whole new perspective on your website

If you’re tired of “browserbating” while building websites then this is for you. Two different viewports in one app and synchronized clicking to boot. It’s pretty darn handy and I use it nearly every single day. Recommend. A++. Would buy again.

View in Mac App Store
  • $4.99
  • Category: Developer Tools
  • Updated: Jan 03, 2014
  • Version: 1.1.6
  • Size: 1.7 MB
  • Language: English
  • Seller: Electric Pulp

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

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