Mobile app specification: structure and example

Short answer

A useful mobile app specification runs 5 to 12 pages, not 50. It should describe the context, the users, the key journeys, the V1 features, the data, the integrations and the constraints (budget, timeline, technical). A spec that's too long hides the real decisions and stops studios from quoting you properly. A short but clear document beats an exhaustive brick that leaves everything open to interpretation.

What a specification is really for

A specification isn't a literary work or a prestige deliverable. It's an operational tool that does three things:

• Align vendors on the same scope so you get comparable quotes.
• Force the client to make decisions before code starts.
• Serve as a contractual reference for what's in and what's out.

If your spec doesn't serve those three functions, it's useless.

The trap of the overlong specification

Plenty of companies hire a consultant who produces an 80-page document with sections like "Target Architecture", "Strategic Vision", "Detailed Level-4 Functional Diagram". Nobody reads the whole thing, not the client, not the vendor.

The result: studios quote by guesswork, the project starts on misunderstandings, change requests pile up. The long document gives a false impression of rigor.

A 5-to-12-page spec, readable in 20 minutes, read twice by the studio before quoting, beats an 80-page document skimmed in 5.

Recommended structure for a useful spec

Section 1: context and goal (1 page)

• Who you are: company, sector, size, stage (early-stage startup, established SMB, larger company).
• Why you're building this app: what problem it solves, for whom.
• The measurable business goal (acquisition, retention, internal productivity, time saved).
• The direct or indirect competition (3 to 5 examples).

Section 2: target users (0.5 to 1 page)

• 2 to 4 personas briefly described: role, context of use, expectations, current friction.
• Expected volumes: how many users in V1, in 6 months, in 18 months.

Section 3: main user journeys (1 to 2 pages)

• Describe the 3 to 5 main journeys in short steps, not specifications.
• Example: "A client creates an account → enters their need → gets 3 proposals → picks one, pays, waits for delivery → leaves a review".
• If you can add clickable Figma wireframes, the vendor will love you for it.

Section 4: V1 features (1 to 2 pages)

A clear list of what's included in V1, organized by module:

• Authentication (email/password, Google, Apple).
• User profile (editing, photo, settings).
• Core feature module (the heart of the app, described in 5 to 10 lines).
• Push notifications.
• Admin back-office (if needed in V1).

For each feature, state what's explicitly OUT of V1. This list of "not-V1" is as valuable as the V1 list.

Section 5: data and integrations (0.5 to 1 page)

• What data is collected, stored, exposed.
• Privacy: personal data, sensitive data, retention periods.
• Third-party integrations: Stripe, payments, notifications, analytics, maps, business services.
• Existing data sources to migrate (Airtable, internal database, another app).

Section 6: constraints (0.5 page)

• Target budget (a range, not an exact number).
• Target timeline and any key event date (launch, trade show, fundraise).
• Imposed technical constraints (stack, hosting, forced integrations).
• Legal constraints (terms of service, licensing, health-data certification for medical).

Section 7: success criteria (0.5 page)

• How you'll measure whether V1 is a success (clear KPIs).
• What a "successful" delivery looks like to you.
• Your expectations for support and maintenance after V1.

The 5 questions a good spec answers

If your spec doesn't clearly answer these 5 questions, rework it before you send it out:

1. Who uses this app and why do they come back?
2. Which main journey absolutely has to work?
3. What are the 3 to 5 features without which the app makes no sense?
4. What's the real budget and the deadline?
5. What is explicitly NOT in the V1 scope?

If you can't answer question 5, your scope will overflow in the first week.

Common mistakes to avoid

Trying to describe the design in the spec. Design happens with a designer, not in a Word doc. Describe the principles (clean, minimal, accessible), not exact colors and detailed screens.

Listing 80 features with no hierarchy. If everything is "must have", nothing is. Cut brutally: 5 to 10 in V1, the rest in a future backlog.

Imposing the stack for no reason. If you write "mandatory stack: Vue.js + MongoDB + Firebase" with no tech expertise behind it, you'll rule out good vendors for nothing.

Confusing a spec with a test plan. The spec says what gets built, not how it's tested. Acceptance criteria come later, during scoping with the vendor.

Writing it for yourself. The spec is read by 3 to 5 different vendors. Write it for them, in language they can understand without knowing your company.

Do you need a spec before contacting a studio?

Not necessarily. Plenty of good projects start with a 2-page brief, or even a 1-hour call, followed by a paid scoping phase with the selected studio.

That scoping phase itself produces the reference document used for development. It costs €1k to €3k and saves 2 to 3 weeks versus writing a spec on your own.

The upside of scoping with a studio: it asks the right technical questions you don't think of internally, and it produces a precise quote at the end. The downside: you tie yourself a bit more to the studio you scope with.

How we do it at Inyka

At Inyka, week 1 of a project is dedicated to strict scoping, paid but deductible if the engagement continues. We produce an 8-to-12-page document with journeys, screens, V1 scope and out-of-V1 scope, integrations, and a schedule. By the end of that week, you know exactly what you're paying, for what, and by when.

If you'd rather show up with a spec already written in-house, we use it as a base and build on it. If you have nothing, we build it together.