How to Write a Mobile App Requirements Document
The quality of your app’s quote, timeline and final product depends heavily on one document written before any design or code. An app requirements document describes what the app must do, for whom and under what constraints, in enough detail for a development team to estimate and build it. A vague brief gets vague estimates that grow later; a clear one gets comparable quotes and fewer surprises.
This guide explains what to include, shows examples of well-written requirements and lists the mistakes we see most often when reviewing briefs for mobile app projects. You do not need to be technical to write a good one.
What an App Requirements Document Is (and Is Not)
An app requirements document, sometimes called a product requirements document (PRD) or software requirements specification (SRS), defines the problem, users, features and constraints of an app. It describes what the app should do, not how developers should code it.
For most startups and SMBs, 8 to 20 pages is enough for a first release. It is a living document: in agile projects it is refined into a backlog as the team learns. It is not a technical architecture document, a visual design or a contract, though it often becomes an appendix to one.
The 10 Sections to Include
A complete requirements document covers business goals, users, features, non-functional needs, integrations and constraints. Use these ten sections as your outline.
- Overview and business goals. The problem, the opportunity and how you will measure success (for example, “500 paying subscribers within six months of launch”).
- Target users and personas. Who uses the app, their context and their main goals. Include every user type: customers, staff, admins, partners.
- Scope. What is in the first release and, just as important, what is explicitly out.
- User journeys. Step-by-step flows for the key tasks, such as sign-up, booking and checkout.
- Functional requirements. Features written as user stories with acceptance criteria, prioritized.
- Non-functional requirements. Performance, security, accessibility, availability, scalability and supported devices.
- Platforms and technical constraints. iOS, Android, web, minimum OS versions, preferred or existing technology.
- Integrations and data. Payment gateways, CRMs, ERPs, maps, existing APIs and data migration.
- Admin, content and reporting needs. What your team must manage and measure after launch.
- Budget, timeline and assumptions. Target launch date, budget range, dependencies and open questions.
How to Write Functional Requirements
Write each feature as a user story with acceptance criteria. This format states who needs the feature, why and exactly how to tell when it is done.
The common user story pattern is: As a [type of user], I want to [action] so that [benefit]. Acceptance criteria then make it testable. Compare a weak and a strong version of the same requirement:
- Weak: “Users can book appointments.”
- Strong: “As a patient, I want to book an available slot with my chosen doctor so that I do not need to phone the clinic. Acceptance criteria: only free slots in the next 30 days are shown; a booking is confirmed on screen and by email within one minute; patients can cancel up to 24 hours before; double bookings are prevented.”
The strong version answers the questions a developer would otherwise ask or, worse, guess at. Then prioritize every story with a simple method such as MoSCoW (Must have, Should have, Could have, Won’t have this time). The “Must have” list defines your MVP; our guide to proof of concept vs prototype vs MVP explains how to keep it lean.
Non-Functional Requirements People Forget
Non-functional requirements describe how well the app must work rather than what it does. They are frequently left out, and they have a big effect on cost.
| Area | Example requirement |
|---|---|
| Performance | Home screen loads within 2 seconds on a 4G connection on a mid-range Android phone. |
| Security | Sensitive data encrypted at rest and in transit; app tested against the OWASP Mobile Top 10. |
| Privacy and compliance | Consent and data deletion flows meet the GDPR for EU users. |
| Accessibility | Meets WCAG 2.2 Level AA principles, supports screen readers and dynamic text sizes. |
| Availability | Backend available 99.9% of the time, excluding planned maintenance. |
| Scalability | Supports 10,000 daily active users at launch, with a path to 100,000. |
| Offline behavior | Users can view past orders and draft forms without a connection. |
| Devices and OS | Supports the current and previous two major iOS and Android versions. |
| Localization | English and Spanish at launch; date, currency and number formats follow the device locale. |
Also note store-related requirements. Apple’s App Store Review Guidelines include rules on sign-in options, account deletion, in-app purchases and privacy disclosures that can shape features, so flag anything that touches payments or user accounts early.
Add Visuals: Wireframes and Flows
Simple sketches remove more ambiguity than pages of text. You do not need polished designs; boxes and arrows are enough.
Include a flow diagram for each key journey and rough wireframes for the main screens. Link to competitor or reference apps and state what you like about each one. If budget allows, a short design sprint producing a clickable prototype lets you test the flow with real users before committing to a build. Our overview of the mobile app design process explains how wireframes evolve into final designs.
Common Mistakes in App Requirements Documents
Most problems come from ambiguity, missing user types and trying to include everything. Watch for these:
- Describing solutions instead of needs. “Use MongoDB” is a technical decision; “store and search 50,000 products” is a requirement. Let the team propose the solution unless you have a real constraint.
- Forgetting the admin side. Someone has to manage users, content, refunds and reports. Admin panels are often 20–30% of the effort.
- Ignoring edge cases. What happens when a payment fails, a user loses connection or two people book the same slot?
- Vague words. “Fast”, “secure”, “user-friendly” and “like Uber” mean different things to different people. Replace them with measurable criteria or specific examples.
- Everything is a must-have. If every feature is priority one, nothing is. Force-rank the list.
- Freezing the document forever. Requirements will change as you learn. Agree how changes are proposed, estimated and approved.
Using the Document to Get Accurate Quotes
Send the same app requirements document to every vendor you are considering, so quotes are comparable. Ask each one to list assumptions and questions.
The questions a vendor asks are a good test of their experience. Expect estimates broken down by feature or phase, which makes it easy to trim scope; our mobile app development cost breakdown shows typical ranges per feature. A detailed document also lets you choose a contract model with confidence. Well-defined scopes suit fixed price, while evolving ones suit time and material, as explained in our comparison of fixed price vs time and material contracts.
Frequently Asked Questions
How long should an app requirements document be?
For an MVP, 8–20 pages including user stories and wireframes is usually enough. Complex, regulated or multi-app platforms may need more, but clarity matters more than length.
Who should write the requirements document?
The product owner or founder should own it, because they understand the business and users. A business analyst or your development partner can help structure it, fill technical gaps and challenge assumptions during a paid discovery phase.
What is the difference between a PRD and an SRS?
A PRD focuses on the product: users, problems, features and success metrics. An SRS is usually more detailed and technical, specifying system behavior and interfaces. Many small teams combine both into one app requirements document.
Do agile projects still need a requirements document?
Yes, though a lighter one. Agile teams still need clear goals, users, scope and priorities to plan sprints and estimate budgets. The document becomes the starting backlog and is refined every sprint.
Turn Your Idea into a Clear Specification
Sigmato’s team in Bengaluru and the UK runs discovery workshops that turn rough ideas into prioritized requirements, user flows and Figma designs ready for estimation. Share what you have, even a one-page outline, and we will help you shape it.
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