swiftui-performance-analyzer

Automatically scans SwiftUI code for performance anti-patterns that cause frame drops and poor scrolling performance.

How to Use This Agent

Natural language (automatic triggering):

• "My SwiftUI app has janky scrolling"
• "Check my code for performance issues"
• "My views are updating too often"
• "App feels slow during scrolling"
• "Review my SwiftUI code for optimization opportunities"

Explicit command:

/axiom:audit-swiftui-performance

What It Checks

Critical Issues (Frame Drops Guaranteed)

1. File I/O in view body — Data(contentsOf:), String(contentsOf:)
2. Creating formatters in view body — DateFormatter(), NumberFormatter()

High Priority (Likely Frame Drops)

3. Image processing in view body — Resizing, filtering, transformations
4. Whole-collection dependencies — .contains(), .filter() on arrays
5. Navigation performance issues — NavigationPath recreation, large models in navigation state

Medium Priority (Performance Degradation)

6. Missing lazy loading — VStack with 100+ items instead of LazyVStack
7. Frequently changing environment values — Updates entire hierarchy every frame
8. Missing view identity — ForEach without explicit id

Low Priority (Optimization Opportunities)

9. Old ObservableObject pattern — Should use @Observable (iOS 17+)

Example Detections

File I/O in View Body

// ❌ BAD: Blocks main thread
var body: some View {
    let data = try? Data(contentsOf: fileURL) // Synchronous I/O!
    if let data, let image = UIImage(data: data) {
        Image(uiImage: image)
    }
}

// ✅ GOOD: Async loading
@State private var imageData: Data?

var body: some View {
    if let imageData, let image = UIImage(data: imageData) {
        Image(uiImage: image)
    }
}
.task {
    imageData = try? await loadImageData()
}

Creating Formatters

// ❌ BAD: Creates every update (1-2ms each)
var body: some View {
    let formatter = DateFormatter() // Expensive!
    formatter.dateStyle = .medium
    Text(date, formatter: formatter)
}

// ✅ GOOD: Static formatter
private static let dateFormatter: DateFormatter = {
    let f = DateFormatter()
    f.dateStyle = .medium
    return f
}()

Performance Risk Score

Calculates risk (0-10):

• CRITICAL issues: +3 points each
• HIGH issues: +2 points each
• MEDIUM issues: +1 point each
• LOW issues: +0.5 points each

Interpretation:

• 0-2: Low risk, good performance
• 3-5: Medium risk, noticeable issues likely
• 6-8: High risk, performance problems expected
• 9-10: Critical risk, poor performance guaranteed

Common Findings

From auditing 100+ SwiftUI apps:

• 70% create formatters in view body
• 50% use VStack instead of LazyVStack for long lists
• 40% have whole-collection dependencies
• 30% do image processing in view body
• 25% have navigation performance issues (NavigationPath recreation, large models)
• 20% have file I/O in view body

Model & Tools

• Model: haiku (pattern matching)
• Tools: Glob, Grep, Read
• Color: purple
• Scan Time: <1 second

Related Skills

For detailed SwiftUI performance optimization:

• swiftui-performance skill — Step-by-step profiling with Instruments 26
• swiftui-debugging skill — Systematic view update diagnosis