How to check if an app is optimized for iPhone Duo
A 30-second test to tell whether an app is running in its old phone layout, has been adapted to the inner display, or is truly built for the fold.
Updated · 2 min read
The App Store does not label apps that are optimized for iPhone Duo. The good news: you can tell in about thirty seconds, with the phone in your hand.
The unfold test
- Open the app on the outer display. Almost every app looks normal here, so this step tells you little on its own.
- Unfold the phone. Watch what happens on the 7.6-inch inner display.
- Read the result:
- The app sits inside black borders, centred on the screen → it has not been rebuilt and is running in its old phone layout. In our directory that is Compatible.
- The app reaches the edges of the inner display → it has been rebuilt with the iOS 27 SDK or later. That is Adapted.
- The app shows a different layout folded and unfolded, puts something useful on each display, supports Split View or does something in the half-open position → it is likely Built for Duo.
Check the App Store page
Apple lets developers upload iPhone Duo screenshots. If a listing shows the app on the unfolded display, the developer intends it to look that way. Screenshots are a statement of intent, though, so they are worth confirming on the phone itself.
The release notes (“What’s New”) are the other place to look. Developers who have done the work usually say so, often naming the inner display, Split View or the outer display. Those notes are one of the sources we link from each listing.
Signs an app was rebuilt but not designed for the fold
Rebuilding with a newer SDK makes an app fill the screen, but it does not make it good at the larger size. Watch for:
- images that are cropped or stretched after you unfold;
- controls that end up awkwardly placed at the edges;
- a single column of content stretched across the whole display.
Apple asks developers not to assume a fixed screen size, because folding and unfolding can resize an app while it is open. Apps that skip that step tend to show these problems.
Skip the testing
That is what this directory is for. Every app here has a tier, the date it was checked and the source for that check. Start with the Built for Duo apps, or browse every app.