If you’re developing a Mac app that runs in the background most of the time (in other words an agent app) you typically don’t want to your app’s icon to consume space on the dock.

Luckily for us, achieving this is quite trivial.  Just follow these steps…

1. In Xcode (4.3 for the purposes of this post), open the Project Navigator (the folder tab under the Run button).
2. Select your project (the parent item with the blue print icon).  This opens the project details view.
3. In the project details view select your app’s main target (under TARGETS) and select the Info tab.
4. If it is not already present add an ‘Application is agent (UIElement)’ item under Custom Mac OS X Application Target Properties.
5. Set this item’s value to YES (as shown below).

And you’re done!

From now on, whenever you execute your app its icon will no longer appear on the Dock or in the Alt + Tab application switcher.