# Run the App Resizability modernization skill in Xcode

> Xcode 27.1 extends its app modernization skill to cover SwiftUI and iPhone Duo, automating part of the mechanical migration.

Source: https://iphoneduosupport.com/checklist/app-resizability-skill/

Severity: polish
Category: tooling
Applies to: swiftui, uikit
Requires: ios-27.1 SDK
Symptom: Manually hunting through a large codebase for fixed sizes and deprecated screen references.
Sources: https://developer.apple.com/videos/play/tech-talks/111461/
Last verified: 2026-09-09

---

Apple's app modernization skill, previously "Modernize your UIKit app", now covers **SwiftUI and iPhone Duo** in Xcode 27.1 under the name **App Resizability**.

## Use it as a first pass

It is good at the mechanical, high-volume work: finding fixed frame sizes, flagging main-screen references, surfacing symmetric safe-area math, pointing at code that will not resize.

It cannot make design decisions. Whether a screen should become a split view, what belongs on the outer display, which actions deserve `.visibilityPriority(.high)` — those need judgement about your product.

A sensible order:

1. Rebuild against the iOS 27.1 SDK.
2. Run App Resizability and review every change it proposes.
3. Work the blocker items on this checklist by hand.
4. Only then consider the new adaptive APIs — arrangements, reserved regions, scene accessories.

## Review its output rather than accepting it

Automated fixes tend to be locally correct and globally bland. Replacing a fixed width with `maxWidth: .infinity` is right in a stack and wrong in a form field that now spans 626 points. Read each change with the surrounding layout in mind.

## How to verify

After running the skill, build and walk the pose matrix. Treat its changes as a starting draft to review, not a completed migration.

---

Published by iPhone Duo Support (https://iphoneduosupport.com). Not affiliated with Apple Inc.