Is your app ready for iPhone Duo?
Apple's first foldable is on sale, and apps built with older SDKs don't fill its inner display. Paste your App Store link and answer seven questions: you'll get a readiness score, the biggest risks and a plan for each team.
free · about two minutes · no sign-up
Only the App Store link or the app's name comes to our server. Your answers are scored in your browser and aren't stored.
What it checks, and how to read the result.
WHAT IT CHECKS
- From the App Store: when the last version came out, whether the app has an iPad layout, whether the release notes mention iPhone Duo, and recent reviews that mention folding.
- From your answers: what happens to a task when the phone opens, testing, size code, the inner and outer displays, screenshots and analytics.
HOW TO USE IT
- 1Paste your App Store link, or type the app's name.
- 2Answer the seven questions. If you don't know an answer, choose "Not sure": that's a finding too.
- 3Share the result with your team. Each step of the plan says which team it's for.
READING THE RESULT
- 75 and above: largely ready. 45 to 74: on the way, with risks. Below 45: not ready yet.
- Losing a task in progress weighs the most, then testing and size code. Screenshots and analytics weigh the least.
- If the version in the App Store predates iPhone Duo, the score stops at 60: your customers don't have the work yet.
WHAT IT DOESN'T DO
- It doesn't open your app. We can't see from outside which SDK it was built with; we estimate it from the release date.
- Only the App Store link or the app's name comes to our server. Your answers are scored in your browser and aren't stored.
- It isn't a test with real users, and it can't replace one.
QUESTIONS WE GET
Do existing apps work on iPhone Duo?
Yes. Every iPhone app runs on it, but how it looks depends on the SDK it was built with. Built with the iOS 26 SDK or earlier, it opens as a smaller window in the middle of the inner display. With the iOS 27 SDK it fills most of the display, and from the iOS 27.1 SDK on, Apple calls it optimised for iPhone Duo.
Which SDK does my app need?
The iOS 27.1 SDK or later, in Xcode 27.1. Only then does the app use the whole display, with toolbars and tab bars standing vertically. Building with the new SDK is the start; the layouts and the fold still need work.
Why do the controls move to the edge on the outer display?
To give content more height when the phone is closed. Controls that usually sit at the top and the bottom move to the right edge, where the thumb reaches them. Wide items, such as a text button or a segmented control, stay in the navigation bar.
How can I test my app for iPhone Duo without the phone?
Use the iPhone Duo simulator in Xcode 27.1, the resizable simulator in Device Hub, or iPhone Mirroring on macOS 27. Go through your key flows in every pose, and fold and unfold in the middle of each one.
Does Fold Check store my data?
No. Only the App Store link or the app's name comes to our server, to read Apple's public data. Your answers are scored in your browser and aren't stored.
How people will use the phone, and what product, design, research, marketing and engineering teams should look at.
Read the note