Fits Duo

Fits Duo tells you whether an iOS app works well on iPhone Duo, Apple’s foldable iPhone. Search for an app and see at a glance how it looks on the inner display: whether it fills the whole screen, uses most of it, or runs in an iPhone-sized window with black bars around it.

Every app gets one clear status: Fits, Partly fits, Should fit, Has issues, Work in progress, Letterboxed, Doesn’t work, or Not verified. Each app page shows that status, the version it applies to, and where it comes from, so you can check it yourself. A version history shows when an app changed, and apps that fit show the version they first fit in.

Owners can add what they see on their own device, which helps others decide before they download or update. If an app isn’t listed yet, ask for it or upvote someone else’s request. The most-voted apps are checked first, and you’ll see a notice when an app you asked for is added.

Browse by category or status to find apps that already make the most of the big screen, or see which of the apps you use every day still show black bars.

Making an iOS app? The developer guides cover what each SDK changes, common layout problems, moving toolbars into the vertical bar, custom bars and sheets, and testing from the command line before you ship an update that fills the inner display.

Over 1,000 apps are listed, in English, Japanese, Simplified and Traditional Chinese, Korean, German, French and Spanish. iPhone Duo goes on sale October 23, 2026.

Fits Duo is free, independent and not affiliated with Apple.