Technical Specification for Mobile Development: What to Include

We deliver turnkey mobile apps and have written over 50 technical specifications. The most common pain point? Vague requirements. A statement like 'the app should be fast and user-friendly' gives the developer no basis to estimate effort, and QA cannot build a test plan. Concrete details such as 'the order list must load within 2 seconds on 4G with 100 concurrent users' provide a baseline. A well-defined specification reduces budget overruns by 20–30% by cutting down clarifying questions during development. Here's what to include to avoid rework.

What Must Be in the Technical Specification

A good specification solves three problems: it lets the developer estimate effort, gives the client acceptance criteria, and serves as a basis for the QA test plan. If the document doesn't cover at least one of these, it's incomplete.

Functional requirements shouldn't be 'user can log in'. Be specific:

• Authentication via email + password, Google Sign-In (google_sign_in / GoogleSignIn SDK), Apple Sign-In (mandatory for iOS if other social logins are available — per App Store Review Guidelines section 4.8).
• Session storage: JWT in flutter_secure_storage / iOS Keychain / Android Keystore, access token lifetime 15 minutes, refresh token 30 days.
• Token expiry behavior: silent refresh via interceptor, do not force user back to the login screen on every launch.

This level of detail eliminates dozens of clarification requests during development.

Critical Non-Functional Requirements

Non-functional requirements (NFR) are often overlooked, yet they directly impact UX. Example table:

Without NFR, developers will implement what's easiest for them, not what the user needs.

How to Describe a Screen in the Technical Specification

Each screen is described using a User Story (As a [role], I want [action] so that [goal]) + wireframe or Figma link + detailed behavior. Not 'profile screen', but:

Screen 'Edit Profile': user can change name (mandatory, 2–50 characters), avatar (choose from gallery or camera, 1:1 crop, max 5 MB), phone number (validation via SMS OTP). Changes saved on 'Save' button tap. If no changes, button is disabled. On network error, show toast with error message; changes are not lost.

Full example: 'Order list loads from API with pagination (20 items per page). Supports pull-to-refresh. Empty state shows placeholder with button 'Create Order'. On network error, show retry button and message. While data is updating, show skeleton loader.'

Poor vs Good Technical Specification Comparison

A proper specification reduces the number of revision cycles by 3x compared to a vague one.

Which API Contracts and Dependencies to Lock Down

The specification should list external dependencies:

• Third-party APIs and SDKs with exact versions (Firebase, Stripe, Google Maps).
• Backend communication format: REST, GraphQL, or WebSocket; authorization scheme (Bearer JWT, API Key, OAuth 2.0).
• If backend is developed in parallel, provide a minimal OpenAPI 3.0 contract for the mobile team.

What Not to Include

Implementation details are the developer's responsibility. The specification describes what should work, not how. 'Use Flutter' is acceptable. 'Use BLoC for state management' is a technical decision to be discussed separately.

Our Process and Timelines

1. Client interview — gather business requirements, roles, priorities.
2. Competitive analysis — study UX patterns of industry leaders.
3. Write the document — functional requirements, NFR, screens, API dependencies.
4. Review and iterate — refine edge cases with the client.

A complete specification takes 2–3 days for an app with up to 20 screens. For complex products (marketplace, fintech) — 4–6 days. Cost is calculated individually after scope assessment.

What Our Work Includes

We deliver a technical specification covering all stages: functional and non-functional requirements, user stories, API contracts, wireframe schemas. The result is a ready document in Markdown or Google Docs. We also advise on interpreting requirements for the mobile platform. Our experience: over 5 years and 50+ projects, guaranteeing removal of ambiguity at the estimation stage.

In a recent case for a delivery client, our technical specification reduced development time by 30% and eliminated contentious points. Contact us to get a consultation on your project and learn how we can help you draft a clear technical specification for your mobile development.

Mobile App Architecture

The app is built in a single ViewController with 2000 lines. Network calls, business logic, UI updates—all in one place. Adding a new feature without regression is difficult, writing a test is impossible. This isn’t “bad code”—it’s a lack of architecture. And it’s more common than you might expect, even in production apps with millions of users.

We design architecture turnkey: from pattern selection to complete project structure with tests and documentation. In 7–10 days you get clean, modular code ready for scaling.

Architecture patterns in mobile solve one problem: separate UI from logic so each part is testable and replaceable.

MVVM: Basic Pattern

Model-View-ViewModel is the standard for iOS (SwiftUI + Combine/async, UIKit + Combine) and Android (Jetpack ViewModel + StateFlow + Compose). The ViewModel holds UI state and business logic. The View only displays state and forwards user intentions to the ViewModel. The Model represents data and its source.

Key rule: ViewModel knows nothing about UIKit or Android View classes. No UIKit imports, no Context dependencies (except Application context through Hilt). This ensures testability: ViewModel is tested as pure Kotlin/Swift code without Android Instrumented Test.

MVVM covers 70% of needs. The remaining 30% require strict feature isolation, team scaling, or complex state management flows.

Clean Architecture: When MVVM Isn’t Enough

Adds layers on top of MVVM:

• Domain layer — business logic, platform-independent. A UseCase (or Interactor) contains a single business rule: GetUserOrdersUseCase, PlaceOrderUseCase. Depends only on interfaces (protocol/interface), not concrete implementations.
• Data layer — repository implementations. OrderRepositoryImpl implements OrderRepository from domain. Knows about Retrofit, Room, UserDefaults. The ViewModel doesn’t know where data comes from—network or cache.
• Presentation layer — ViewModel + View. Knows about Domain, not Data.

Dependency rule: dependencies point inward only. Domain depends on nothing. Data and Presentation depend on Domain.

Presentation → Domain ← Data

This allows swapping implementations: tests use an in-memory repository instead of network, the interface remains the same.

Practical caveat: Clean Architecture adds files and layers. For small apps, this is overhead. It’s justified starting from ~15 features and teams of 3+ developers.

BLoC for Flutter: Predictable State Flow

BLoC (Business Logic Component) is the standard pattern in the Flutter community. The flutter_bloc library implements it with two types: Bloc (Event → State) and Cubit (State without Events, only methods).

Bloc processes Event and emits a new State via on<EventType> handlers. State is immutable—a new object for each change. BlocBuilder re-renders only the part of the tree where state changed.

// Event
abstract class CartEvent {}
class AddItemToCart extends CartEvent {
  final String productId;
  AddItemToCart(this.productId);
}

// State
abstract class CartState {}
class CartLoaded extends CartState {
  final List<CartItem> items;
  CartLoaded(this.items);
}

// Bloc
class CartBloc extends Bloc<CartEvent, CartState> {
  CartBloc(this._cartRepository) : super(CartLoaded([])) {
    on<AddItemToCart>(_onAddItem);
  }

  Future<void> _onAddItem(AddItemToCart event, Emitter<CartState> emit) async {
    final current = state as CartLoaded;
    final updated = await _cartRepository.addItem(event.productId);
    emit(CartLoaded(updated));
  }
}

The advantage of BLoC is testability. blocTest from the bloc_test package allows you to verify: given a certain Event and initial State, the BLoC should emit a certain State. No UI, no mocks for the Flutter framework.

VIPER: For Large iOS Projects

VIPER (View, Interactor, Presenter, Entity, Router) is the strictest separation of responsibilities for iOS. Each component has a protocol and concrete implementation.

• View — UI only, delegates everything to Presenter
• Interactor — business logic, network and data operations
• Presenter — mediator between View and Interactor, formats data for View
• Entity — data models (pure structures)
• Router — navigation between modules

Each module (screen or feature) is a separate VIPER module. This eliminates coupling between features and allows large teams to work in parallel without conflicts.

The cost: many files, many protocols. Boilerplate is generated via Sourcery or custom Xcode templates. VIPER is justified for apps with 10+ developers and 50+ screens.

TCA (The Composable Architecture)

TCA by Point-Free is a more modern alternative to VIPER for iOS/macOS. Core concepts: State (immutable feature state), Action (all possible events), Reducer (State + Action → new State + Effect), Store (holds State, processes Actions).

Scope allows composable building of large features from small ones: a parent Reducer delegates part of State to a child. Each feature is tested in isolation via TestStore with precise control over Effects.

TCA has a steep learning curve but provides predictability that is hard to achieve otherwise: every state change is an explicit Action with a specific source.

Which Pattern to Choose for Your Project?

We’ll evaluate your project in 1 day—choose an architecture considering team size, platform, and growth plans.

There is no universal answer. Architecture is chosen based on team size, testability requirements, and app support horizon.

What Components Are Included in Our Architecture Work?

• Audit of current architecture (if the app already exists)—identify bottlenecks and regression areas.
• Design of modular structure with clear layer boundaries and dependency rules.
• Creation of project scaffold with DI setup, folder organization, and linter configuration.
• Writing unit tests for domain layer and ViewModel—minimum 80% coverage of key use cases.
• Preparation of documentation—architecture diagrams, README with code modification rules, onboarding guide for new developers.
• Delivery of a working repository with CI pipeline (GitHub Actions / Bitrise) configured to run tests and static analysis.

All this is included in the design cost. Additionally, support during implementation: team consultations, code review of first pull requests.

How Does Lack of Architecture Affect Development Speed?

Typical scenario after 18 months without architecture: 40% of development time goes to debugging regressions. A new developer spends a week understanding the code before making their first PR. Tests aren’t written “because it’s hard to mock.” Adding a new feature requires understanding half the codebase.

Choosing architecture at the start is an investment that pays off in 3–6 months. According to our data, a properly designed architecture with MVVM + Clean gives 3x fewer regressions compared to a monolithic ViewController. And the cost of implementation is recouped in 2–3 sprints.

According to Apple’s recommendations, separation of responsibilities is a key factor in code stability.

Why Trust Our Team with Architecture?

An incorrect pattern choice at the start leads to rewriting half the code a year later. We’ve seen dozens of projects where trying to save on architecture resulted in months of refactoring. With over 10 years of commercial development experience and work on apps from 1 to 50 developers, we help avoid common mistakes:

• Overengineering for a simple MVP (we assign MVVM, not VIPER).
• Lack of dependency injection—we integrate Hilt/Koin/Dagger from the start.
• Ignoring testability—we establish protocols/interfaces from the first commit.

We’ve architected over 200 mobile applications for startups and enterprises, with guaranteed 80%+ test coverage and CI/CD pipelines. Our team holds certifications in iOS and Android development, and we follow the App Store Review Guidelines (Section 4.2/5.1) to ensure smooth store approvals.

Start with a free architecture audit — send us your project description and we’ll deliver a tailored architecture plan within 24 hours. Reach out via Telegram or email to get started.