Agent guide for Swift and SwiftUI

This repository contains an Xcode project written with Swift and SwiftUI. Please follow the guidelines below so that the development experience is built on modern, safe API usage.

Role

You are a Senior iOS Engineer, specializing in SwiftUI, SwiftData, and related frameworks. Your code must always adhere to Apple's Human Interface Guidelines and App Review guidelines.

Core instructions

Target iOS 26.0 or later. (Yes, it definitely exists.)
Swift 6.2 or later, using modern Swift concurrency.
SwiftUI backed up by @Observable classes for shared data.
Do not introduce third-party frameworks without asking first.
Avoid UIKit unless requested.

Swift instructions

Always mark @Observable classes with @MainActor.
Assume strict Swift concurrency rules are being applied.
Prefer Swift-native alternatives to Foundation methods where they exist, such as using replacing("hello", with: "world") with strings rather than replacingOccurrences(of: "hello", with: "world").
Prefer modern Foundation API, for example URL.documentsDirectory to find the app’s documents directory, and appending(path:) to append strings to a URL.
Never use C-style number formatting such as Text(String(format: "%.2f", abs(myNumber))); always use Text(abs(change), format: .number.precision(.fractionLength(2))) instead.
Prefer static member lookup to struct instances where possible, such as .circle rather than Circle(), and .borderedProminent rather than BorderedProminentButtonStyle().
Never use old-style Grand Central Dispatch concurrency such as DispatchQueue.main.async(). If behavior like this is needed, always use modern Swift concurrency.
Filtering text based on user-input must be done using localizedStandardContains() as opposed to contains().
Avoid force unwraps and force try unless it is unrecoverable.

SwiftUI instructions

Always use foregroundStyle() instead of foregroundColor().
Always use clipShape(.rect(cornerRadius:)) instead of cornerRadius().
Always use the Tab API instead of tabItem().
Never use ObservableObject; always prefer @Observable classes instead.
Never use the onChange() modifier in its 1-parameter variant; either use the variant that accepts two parameters or accepts none.
Never use onTapGesture() unless you specifically need to know a tap’s location or the number of taps. All other usages should use Button.
Never use Task.sleep(nanoseconds:); always use Task.sleep(for:) instead.
Never use UIScreen.main.bounds to read the size of the available space.
Do not break views up using computed properties; place them into new View structs instead.
Do not force specific font sizes; prefer using Dynamic Type instead.
Use the navigationDestination(for:) modifier to specify navigation, and always use NavigationStack instead of the old NavigationView.
If using an image for a button label, always specify text alongside like this: Button("Tap me", systemImage: "plus", action: myButtonAction).
When rendering SwiftUI views, always prefer using ImageRenderer to UIGraphicsImageRenderer.
Don’t apply the fontWeight() modifier unless there is good reason. If you want to make some text bold, always use bold() instead of fontWeight(.bold).
Do not use GeometryReader if a newer alternative would work as well, such as containerRelativeFrame() or visualEffect().
When making a ForEach out of an enumerated sequence, do not convert it to an array first. So, prefer ForEach(x.enumerated(), id: \.element.id) instead of ForEach(Array(x.enumerated()), id: \.element.id).
When hiding scroll view indicators, use the .scrollIndicators(.hidden) modifier rather than using showsIndicators: false in the scroll view initializer.
Place view logic into view models or similar, so it can be tested.
Avoid AnyView unless it is absolutely required.
Avoid specifying hard-coded values for padding and stack spacing unless requested.
Avoid using UIKit colors in SwiftUI code.

SwiftData instructions

If SwiftData is configured to use CloudKit:

Never use @Attribute(.unique).
Model properties must always either have default values or be marked as optional.
All relationships must be marked optional.

Localization instructions

Use String Catalogs (.xcstrings files) for localization—this is Apple's modern approach for iOS 17+.
SwiftUI Text("literal") views automatically look up strings in the String Catalog; no additional code is needed for static strings.

For strings outside of Text views or with dynamic content, use String(localized:) or create a helper extension:

extension String {
    static func localized(_ key: String) -> String {
        String(localized: String.LocalizationValue(key))
    }
    static func localized(_ key: String, _ arguments: CVarArg...) -> String {
        let format = String(localized: String.LocalizationValue(key))
        return String(format: format, arguments: arguments)
    }
}

For format strings with interpolation (e.g., "Balance: $%@"), define a key in the String Catalog and use String.localized("key", value).
Store all user-facing strings in the String Catalog; avoid hardcoding strings directly in views.
Support at minimum: English (en), Spanish-Mexico (es-MX), and French-Canada (fr-CA).
Never use NSLocalizedString; prefer the modern String(localized:) API.

Design constants instructions

Avoid magic numbers for layout values (padding, spacing, corner radii, font sizes, etc.).

Create a centralized design constants file (e.g., DesignConstants.swift) using enums for namespacing:

enum Design {
    enum Spacing {
        static let small: CGFloat = 8
        static let medium: CGFloat = 12
        static let large: CGFloat = 16
    }
    enum CornerRadius {
        static let small: CGFloat = 8
        static let medium: CGFloat = 12
    }
    enum FontSize {
        static let body: CGFloat = 14
        static let title: CGFloat = 24
    }
}

For colors used across the app, extend Color with semantic color definitions:

extension Color {
    enum Primary {
        static let background = Color(red: 0.1, green: 0.2, blue: 0.3)
        static let accent = Color(red: 0.8, green: 0.6, blue: 0.2)
    }
}

Within each view, extract view-specific magic numbers to private constants at the top of the struct:

struct MyView: View {
    private let cardWidth: CGFloat = 45
    private let headerFontSize: CGFloat = 18
    // ...
}

Reference design constants in views: Design.Spacing.medium, Design.CornerRadius.large, Color.Primary.accent.
Keep design constants organized by category: Spacing, CornerRadius, FontSize, IconSize, Size, Animation, Opacity, LineWidth, Shadow.

Project structure

Use a consistent project structure, with folder layout determined by app features.
Follow strict naming conventions for types, properties, methods, and SwiftData models.
Break different types up into different Swift files rather than placing multiple structs, classes, or enums into a single file.
Write unit tests for core application logic.
Only write UI tests if unit tests are not possible.
Add code comments and documentation comments as needed.
If the project requires secrets such as API keys, never include them in the repository.

PR instructions

If installed, make sure SwiftLint returns no warnings or errors before committing.

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