Twelve Twenty, the Dutch maker of the print-size checking OS X app Will It Fit and the iOS calendaring tool Get Together, recently published their third app, Uberlayer. Uberlayer is a small tool for UI and web designers on Mac OS X to quickly overlay images of a new design work onto your desktop.

Let’s say you just designed a mockup of an update to an existing website or application. Drop it onto Uberlayer to bring it on the screen. Using shortcuts you can move it around in pixel steps, make it more or less transparent, and activate click-through options. If you make the design half-transparent and you have the current version of an app or website just behind it, you can easily check how the current design changes will affect the overall look of the whole product. Using the click-through option, it’s easy to select certain parts you want to change to copy or delete them in the “real” version of your product.

I tried Uberlayer on my personal website by trying out a different style for an ad I currently have on it. This is what a half transparent “uberlayed” image looks like:

It’s actually pretty hard to describe how the app works using only words and pictures. If you’re curious, I recommend you head over the Twelve Twenty website and check out their Uberlayer demo video. I think Uberlayer can be a useful tool in a web or application designer’s workflow. Uberlayer is $1.99 on the Mac App Store.