Modular iOS Architecture: When and How to Split an App

Know why you are modularizing

Start with a measurable problem. Common reasons include slow builds, unclear feature ownership, accidental dependencies, difficult testing or multiple applications sharing the same capabilities.

If the app is small and the team moves quickly inside one target, folders and dependency rules may be enough. Introduce a module when independent compilation, reuse or enforced visibility provides real value.

Find boundaries in product language

Good modules often match stable product concepts: Authentication, Search, Booking, Payment, Profile or DesignSystem. These names are easier to reason about than broad technical buckets such as “Managers” or “Utilities.”

Keep the dependency graph directional

A module graph should be understandable without opening every file. Feature modules may depend on small core abstractions, while core modules should not know about features.

App
 ├── FeatureSearch
 ├── FeatureBooking
 ├── FeaturePayment
 ├── DesignSystem
 ├── Networking
 └── DomainModels

Avoid a giant shared module that becomes the place for anything used twice. Shared code should have a coherent responsibility and a stable API.

Design small public interfaces

Visibility is one of the biggest benefits of modules. Keep implementation details internal and expose only the entry point, domain contracts or models needed by consumers.

public protocol BookingFeatureFactory {
    @MainActor
    func makeBookingFlow(input: BookingInput) -> AnyView
}

A small public surface makes refactoring safer. If another feature imports internal view models or DTOs, the boundary is not doing its job.

Choose packages and targets pragmatically

Swift Package Manager works well for many internal modules because dependencies and resources can be declared clearly. Xcode targets may still be appropriate when you need application-specific capabilities or tighter integration with an existing workspace.

Choose one approach that your team can maintain. The architectural boundary matters more than whether the module is represented by a package or a framework target.

Handle resources and configuration explicitly

Feature modules often own localized strings, assets and previews. Keep these resources close to the feature while allowing the host application to provide environment configuration and brand-specific values.

• Do not let modules read global singletons for environment settings.
• Inject URLs, feature flags and analytics abstractions.
• Keep secrets outside source code and packages.
• Test resource loading in both development and archive builds.

Migrate one feature at a time

1. Select a feature with clear boundaries and frequent change.
2. Remove reverse dependencies from shared code back into the feature.
3. Define the feature’s public entry point.
4. Move code and resources while keeping behavior unchanged.
5. Add module-level tests and measure build impact.
6. Repeat only where the result is beneficial.

Incremental migration reduces risk and teaches the team which boundaries actually fit the product.

Modularization checklist

• Each module has one clear reason to change.
• The dependency graph has no cycles.
• Public interfaces are intentionally small.
• Features can be tested without launching the entire app.
• Shared modules are cohesive, not dumping grounds.
• The module improves delivery more than it adds ceremony.