ios-launch-performance

iOS Launch Performance

Use this skill to review the path from an app launch request to first visible UI and early responsiveness.

Focus on work that happens:

• before main
• during UIKit or SwiftUI startup
• inside UIApplicationDelegate, UISceneDelegate, or SwiftUI App
• during root UI creation
• before the first visible frame
• before the first meaningful interaction
• during early post-launch work that still affects user-perceived readiness

This is not a general iOS performance skill. Use it only when the issue is launch-specific or when the code runs on the launch path.

Core Model

Treat launch as a pipeline with separate phases:

1. Process creation and system preparation
2. dyld loading, binding, fixups, runtime registration, and static initialization
3. UIKit or SwiftUI runtime startup
4. App-level initialization in UIApplicationDelegate, UISceneDelegate, or SwiftUI App
5. Launch orchestration and dependency setup
6. Root UI construction, layout, drawing, and first frame commit
7. Early post-launch work that affects responsiveness
8. Later feature-specific or maintenance work

Do not optimize blindly. First identify which phase is expensive, then recommend changes that move, remove, lazy-load, parallelize, serialize, or measure that specific work.

When to Use This Skill

Use this skill when the task involves:

• slow app launch
• startup regressions
• cold, warm, or prewarmed launch
• resume-vs-launch confusion
• first-frame readiness
• early responsiveness after launch
• pre-main or dyld work
• Objective-C +load, +initialize, constructor functions, or static initialization
• AppDelegate or SceneDelegate startup work
• SwiftUI @main App, WindowGroup, root view setup, or environment injection
• dependency container setup during launch
• launch orchestrators or ordered startup steps
• third-party SDK initialization during launch
• framework linking strategy when launch cost is suspected
• launch metrics from Instruments, XCTest, MetricKit, or Xcode Organizer