This looks like a neat tool, with a nice simple solution to a common UI development problem.
What image file formats can be used as mockups?
What image file formats can be used as mockups?
One feature request would be to make the app automatically refresh the overlay when the source file changes, or to have a keyboard shortcut to refresh from the saved file. This would be useful when toggling layers on/off in Photoshop to look at different states of a screen. Cheers!