You can quickly compare your app/website with the designs as an overlay, using the Pop Out feature.
Click on the Pop Out button on the bottom left or simply use the shortcut ⌘O on the Mac app or Alt+O on the Windows app.
💁♀️ Pop Out is only available on desktop apps, but we're looking to add this to the Web app soon!
Snap to simulator
On the Mac app, you can click the Phone icon on the bottom to directly snap the Pop Out to simulator in Xcode.
☝️ To be able to use the Snap to simulator feature, Zeplin's Mac app needs to have Screen Recording permission on your Mac.