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:
| Parameter | Sample Requirement |
|---|---|
| Performance | Cold start ≤ 3 seconds on iPhone XR and Pixel 5 |
| Network timeout | Connect timeout 10s, receive timeout 30s |
| Offline | Last 50 records available without internet |
| App size | IPA ≤ 50 MB before resource download (App Thinning) |
| Supported OS versions | iOS 15+, Android 8.0+ (API 26+) |
| Localization | ru, en mandatory; de, fr next release |
| Accessibility | Support Dynamic Type (iOS) and font scale (Android) |
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
| Aspect | Poor Example | Good Example |
|---|---|---|
| Screen | 'Profile screen' | Full behavior description with validation |
| Performance | 'Fast' | 'Cold start < 3s, API response time < 1s' |
| Offline | 'Works without internet' | 'Last 50 records available offline' |
| Authentication | 'Social login' | 'Google Sign-In, Apple Sign-In, email+password with JWT' |
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
- Client interview — gather business requirements, roles, priorities.
- Competitive analysis — study UX patterns of industry leaders.
- Write the document — functional requirements, NFR, screens, API dependencies.
- 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.