Mobile App Requirements Document: How to Write One That Works

A mobile app requirements document is the single most important deliverable before development begins. It aligns stakeholders, prevents scope creep, reduces costly mid-project changes, and gives your development team a clear roadmap.

Yet most app projects still start with vague briefs and verbal conversations. The result: missed deadlines, budget overruns, and an app that does not match what anyone envisioned. This guide walks you through how to write a requirements document that your team will actually use.

What Is a Mobile App Requirements Document?

A mobile app requirements document (also called a Product Requirements Document or PRD) is a structured document that defines what your app should do, who it is for, and how it should behave. It serves as the contract between stakeholders and the people building the app.

PRD vs BRD vs SRS: Which Do You Need?

For most mobile app projects, a PRD is sufficient. It combines business context with functional requirements in a format that both business and technical teams can understand.

How to Write a Mobile App Requirements Document (9 Steps)

Step 1: Define Your App Vision and Objectives

Start with the big picture. Answer three questions clearly:

• What problem does this app solve?
• Who is the target user?
• What does success look like? (Define 2-3 measurable goals.)

Write a one-sentence elevator pitch: “[App name] helps [target users] to [solve this problem] by [key feature/approach].” This sentence anchors every decision that follows.

Step 2: Conduct Market Research and Competitive Analysis

• Identify 3-5 direct competitors and analyse their features, ratings, and user reviews.
• Note what competitors do well and where their users complain.
• Identify your unique value proposition: what will your app do differently or better?
• Document market size and trends relevant to your app category.

Step 3: Create User Personas and User Stories

User personas are fictional representations of your target users, based on real research. For each persona, document:

• Demographics: Age, location, profession, tech savviness.
• Goals: What they want to accomplish with your app.
• Pain points: Frustrations with current solutions.
• Behaviour: How, when, and where they would use your app.

Then write user stories in the format: “As a [persona], I want to [action] so that [benefit].” Learn more about mapping user paths in our guide on user flows in UX design.

Step 4: List and Prioritise Features (MoSCoW Method)

Step 5: Document Functional Requirements

Functional requirements describe what the app does. For each feature, document:

• Feature name and description.
• User actions (inputs): What the user does.
• System responses (outputs): What the app does in return.
• Edge cases: What happens when something goes wrong.
• Acceptance criteria: Specific conditions for the feature to be considered complete.

Step 6: Define Non-Functional Requirements

Performance: App should load within 2 seconds. API responses under 500ms.

Scalability: System should handle 10,000 concurrent users at launch, with capacity to scale to 100,000.

Security: Data encryption at rest and in transit. Biometric authentication support. Compliance with PDPA (Singapore).

Availability: 99.9% uptime target.

Compatibility: Support iOS 16+ and Android 12+. Screen sizes from 4.7″ to 6.7″.

Step 7: Specify UI/UX and Design Requirements

• Include wireframes or low-fidelity mockups for key screens.
• Define the navigation structure (tab bar, drawer, bottom navigation).
• Specify brand guidelines: colours, typography, iconography.
• Note accessibility requirements (WCAG 2.1 AA for mobile).

For guidance on mobile design, read our mobile app development process guide.

Step 8: Set Technical Specifications

• Target platforms: iOS, Android, or both. Native, hybrid, or cross-platform (React Native, Flutter).
• Backend architecture: Cloud provider, database choice, API design (REST vs GraphQL).
• Third-party integrations: Payment gateways (Stripe, PayNow), analytics (Firebase, Mixpanel).
• Device features required: Camera, GPS, Bluetooth, biometrics, NFC.

Choosing between native and cross-platform? Read our comparison of native vs cross-platform apps.

Step 9: Establish Budget, Timeline, and Constraints

• Define the total budget and break it into phases (design, development, testing, launch).
• Set realistic milestones with dates.
• List known constraints: regulatory requirements, third-party dependencies, team availability.

For Singapore-specific cost guidance, see our article on the cost of developing an app in Singapore.

Often-Overlooked Sections That Matter

Admin Panel and Backend Requirements

Most requirements documents focus on the user-facing app and forget the admin panel. Document what administrators need: user accounts, content management, orders, analytics dashboards, push notification management, and role-based access control.

Data Privacy and Compliance

• PDPA (Singapore): Consent collection, data access requests, breach notification procedures.
• GDPR (if serving EU users): Data portability, right to be forgotten, cookie consent.
• Industry-specific: PCI DSS for payments, HIPAA for health data.

Accessibility Standards

• Follow WCAG 2.1 AA guidelines for mobile.
• Support screen readers (VoiceOver for iOS, TalkBack for Android).
• Ensure touch targets are at least 44×44 points.

Our web accessibility guide covers compliance standards in detail.

App Store Submission Requirements

• Apple App Store: App Review Guidelines compliance, privacy nutrition labels, app preview screenshots.
• Google Play: Target API level requirements, data safety section, content rating questionnaire.

Post-Launch Maintenance and Roadmap

• Maintenance plan: Who handles bug fixes, OS updates, and server monitoring post-launch?
• Update frequency: How often will you release new versions?
• Feature roadmap: What “Should Have” features will be added in future releases?

Budget for ongoing costs using our guide on website maintenance cost in Singapore.

Best Tools for Writing App Requirements

7 Common Mistakes to Avoid

• Writing requirements that are too vague. “The app should be fast” is not a requirement. “Pages should load within 2 seconds on a 4G connection” is.
• Skipping user research and writing requirements based on assumptions.
• Including implementation details. Describe what, not how.
• Ignoring non-functional requirements (performance, security, scalability).
• Not involving developers early for feasibility feedback.
• Treating the document as final. Build in a change management process.
• Forgetting the admin panel, analytics, and post-launch maintenance.

Frequently Asked Questions

How long should a mobile app requirements document be?

It depends on complexity. A simple app PRD might be 5-10 pages. A complex enterprise app could be 30-50+ pages. Focus on clarity and completeness rather than length.

Who is responsible for writing the requirements document?

Typically the product manager or product owner. The key is that one person owns the document, but input comes from stakeholders, designers, and developers.

How do you handle changing requirements?

Use a change request process. Any change should be documented with the reason, impact on timeline/budget, and approval from stakeholders.

What is the difference between functional and non-functional requirements?

Functional requirements describe what the app does (features, actions, responses). Non-functional requirements describe how it performs (speed, security, scalability).

Key Takeaways

• A good requirements document prevents scope creep, budget overruns, and misaligned expectations.
• Follow the 9-step process: vision, research, personas, features, functional, non-functional, UI/UX, tech specs, budget.
• Do not skip non-functional requirements, admin panel specs, PDPA compliance, and accessibility.
• Use MoSCoW to ruthlessly prioritise features for your MVP.
• Treat the document as a living reference, not a one-time deliverable.

Need Help With Your App Project?

At MediaPlus Digital, we help Singapore businesses plan and build mobile apps from concept to launch. Explore our mobile app development services or contact us to discuss your project.