I design and build iOS apps for the iPhone Duo, iPhone and iPad. My own app, ShellDrop, is a native SSH terminal that runs on all three, closed or open on the Duo. I'm developing it for the iPhone Duo on iOS 27 right now, and the notes below come from that work.
- Who it's for
- Anyone, anywhere, who wants an iOS app designed and built for the iPhone Duo, iPhone and iPad.
- Format
- Every screen designed for each of the Duo's positions, built on iOS 27 with the latest Xcode, and tested in every position before the next round of changes.
- Includes
- New apps, and redesigns of existing iOS apps for the Duo.
- Price
- Quoted against scope.
Designing for every position of the iPhone Duo
Every screen of an iPhone Duo app needs a layout for each position the device can be in:
- Open, closed, landscape and portrait
- Open landscape and portrait
- Split screen landscape and portrait
- The half-closed state
Getting the design right in all of those positions takes a lot of testing. It's also what makes the device interesting to design for: having multiple positions like this really allows you to bring an app to life.
Redesigning an existing iPhone app for the Duo
An app that already runs on iPhone is the starting point for a Duo redesign. Each existing screen is designed again for every position in the list above, from closed in portrait through to split screen and half-closed, and then tested in each of them. Where the app also runs on iPad, the same app can carry all three devices, the way ShellDrop does.
Accessibility across every position
On the Duo, a screen that reads well closed has to read just as well open, in split screen and half-closed. Accessibility checks go into the same testing as the layouts, position by position, on every screen.
Thoughts on iOS app design in late 2026
- App design is now a communication problem. The quality of an app comes down to how well the vision can be described to the agent in words. Most of my time on ShellDrop goes on working out effective ways to describe what I want, in detail, in English, so the agent can get as much done as possible, as quickly and as completely as possible.
- Literally anything is possible. You can do anything you want with an app. What it comes down to is the time put into creating it, refining it and maintaining it.
- The models are fast. Opus 5.5 writes the code, and it does it quickly. This will probably be out of date in about two weeks.
- iOS 27 means upgrading everything. Building for the Duo meant moving every operating system, Xcode and the rest of the toolchain to the latest versions first.
- The Duo needs a lot of testing. Each position in the list above is a separate layout to check, on every screen.
The longer version is in the post App design is now a communication problem.
How I build iOS apps
iPhone app design here starts with words. I describe the design and the agent builds it. The code is written by an AI coding agent running on my own agent operating system, and my time goes on the vision: what each screen does, how it looks in each position, and how it moves. Every build is then tested in each position before the next round of changes.
ShellDrop
ShellDrop is a free iOS terminal for connecting to a Mac or server over SSH, attaching to tmux, and steering AI coding agents such as Claude Code and Codex from a phone. It runs on iPhone, on the iPhone Duo closed or open, and on iPad, including the 13-inch iPad Pro with a hardware keyboard. How I use it day to day is in running AI agents from an iPhone.
Tell me about the app.
Describe what the app does and who it's for, and I'll come back with a quote against scope.
Talk about your app →Questions about app design for iPhone Duo
What is different about app design for the iPhone Duo?
The number of positions the device can be in. An iPhone Duo app has to work open and closed, in landscape and portrait, in split screen, and half-closed, and each of those is its own layout to design and test.
Which iOS version do you build iPhone Duo apps on?
iOS 27, with the latest Xcode. Developing for the Duo meant upgrading everything first: the operating systems on every device, Xcode, and the rest of the toolchain.
Can you redesign an existing iOS app for the iPhone Duo?
Yes. The existing screens are the starting point, and each one is designed again for the Duo's positions and then tested in every one of them.
Do you design for iPhone and iPad as well?
Yes. ShellDrop runs on iPhone, iPhone Duo and iPad from the same app, and client apps can be built the same way.
Apps built for a business's own staff, replacing the subscription software it pays for, are covered on agent services for businesses.