Mobile App Requirements Specification
A Requirements Specification (SRS — Software Requirements Specification) is a more formal document than a technical specification. While a spec describes "what the customer wants", SRS formalizes it into a structure that can be traced: from business requirement → system requirement → test case. Needed by teams with defined processes or when app is developed under contract with SLA.
SRS structure for mobile application
IEEE 830 standard defines a basic structure, but it's adapted for mobile development. Key sections:
1. Overview
- Product purpose and target audience
- Context diagram: app as a "black box" with external actors (user, backend API, payment system, push service)
- Platform constraints: iOS 15+ / Android 9+ (API 28+), supported devices
2. Functional Requirements
Each requirement — atomic, verifiable, traceable:
FR-AUTH-001: App must support email and password authentication. FR-AUTH-002: App must support Sign in with Apple on iOS (mandatory if other OAuth providers exist — App Store Guideline 4.8). FR-AUTH-003: Session must be restored automatically on app launch if refresh token not expired.
Numbering by functional blocks: FR-AUTH-*, FR-PAYMENT-*, FR-PROFILE-*. Traceability: each FR code references User Story or business requirement.
3. Non-functional Requirements
Classified by ISO 25010:
-
Performance:
NFR-PERF-001: API response time must not exceed 2 seconds at 95th percentile under 500 RPS load -
Security:
NFR-SEC-001: Authorization tokens stored in iOS Keychain / Android Keystore, not in SharedPreferences -
Accessibility:
NFR-ACC-001: All interactive elements have accessibility labels for VoiceOver (iOS) and TalkBack (Android) support -
Portability:
NFR-PLAT-001: App supports iPhone SE 2nd gen (4.7") and Samsung Galaxy A32 as minimum target devices
4. Data models and business rules
Not backend ER diagram, but entity description from client perspective: which fields UI displays, which validations apply on client, which compute locally.
5. Use Cases
UML Use Case format or Gherkin (Given / When / Then) for complex scenarios. Gherkin is useful as it directly converts to acceptance tests:
Scenario: Successful class booking
Given user is authorized
And user has active pass with remaining > 0
When user selects class with free spots
And presses "Book"
Then class appears in "My bookings"
And pass balance decreases by 1
And user receives push notification with confirmation
6. External interfaces
List of integrations with specific SDKs and versions:
- Firebase Cloud Messaging SDK 10.x — push notifications
- Stripe iOS SDK 23.x / Stripe Android SDK 20.x — payments
- Google Maps SDK 5.x (Android), 8.x (iOS) — mapping features
SRS vs. spec in practice
Spec — working document for team, can be informal. SRS — contract document with clear numbering, traceability and acceptance criteria. SRS needed if:
- Development by outsourced teams with fixed price per scope
- Product passes certification (medical apps, licensed fintech)
- QA team works by formal test plans with requirement traceability
Timeline
SRS for 15–25 screen app: 2–3 days. For complex products with multiple roles, integrations and compliance requirements: 4–6 days. Cost calculated individually after analyzing functionality scope.