How to make an app: the seven decisions between an idea and both app stores

Settle two things before anything is built: whether the idea needs an app at all (a website, a spreadsheet or a group chat is often the honest answer), and what the one job is that the app does on an ordinary day. The test is a sentence — “[who] uses it to [do what] when [moment]” — and a week of asking people in that moment whether they would. I have an app idea, now what is the page; how to test an app idea before you build is the week; how to find a mobile app idea is for the case where the idea is still forming.

Everything after this step reads one document: who the app is for, the one job, the five to eight screens, what each screen must do to count as done, what is deliberately out, and the two platforms. It is the same document whether a developer, an agency or an AI agent builds it, and it is the thing that turns quotes from guesses into numbers. The PRD prompt produces it from six questions; the app requirements document template is the long form; mobile app prototyping is how to decide which parts to draw before you write.

The default this site argues for is both in the spec from day one, with the launch order a separate decision: the PRD is platform-neutral, so nothing is lost by writing it for both, and a great deal is lost by discovering the second platform is a second project. iOS or Android first has the cases where one platform first is right. Two things are fixed whichever you pick: the Apple Developer Program is $99 a year and Google Play is a one-time $25, and each store reviews the app before it goes live.

Four routes, and the PRD is the input to all of them. A developer or an agency, quoted on the PRD. A cross-platform framework (React Native, Flutter), which is one codebase in a third language — React Native vs native settles whether that suits your product. A web app in a store wrapper, which is fast when a website already exists and has a rule to meet — turn a website into an app. Or native on both platforms with an AI agent, where the PRD is the first prompt: in Modaal, Plan mode returns “a structured implementation plan (a feature spec) without writing code”, you approve it, and the agent writes the SwiftUI and Jetpack Compose from one project on your Mac; the Free plan covers one project with unlimited prompts on one platform, and Pro (€9 per user per month billed annually, €15 monthly) adds both platforms and TestFlight — /pricing. How to choose an AI mobile app builder is the comparison; best native app builders is the one that defines “native”. The platform-specific routes are how to make an iPhone app and how to build an Android app.

The first version is the five to eight screens in the PRD and nothing else; the login screen, the settings page and the AI feature are the usual candidates for version two. Two decisions that look like features and are really scope: whether the app charges money, and how — how to monetize your mobile app and, if it does, paywall tools for iOS and Android; and whether it needs a backend at all in version one — how to build a mobile app from scratch has the rule for when a scenario demands one.

Simulators find layout problems; phones in other people’s hands find the product problems. On iPhone the mechanism is TestFlight, on Android the Play Console’s testing tracks, and both need the store accounts from decision three opened early rather than at launch. The spec from decision two is the test script: each screen’s “done” line is a thing a tester either could or could not do. Mobile app security is the checklist to run before strangers have the build.

Both stores review before release, and the reasons apps are sent back are known in advance — App Store rejection reasons has Apple’s guideline text, and how to publish an app on the App Store is the submission itself, step by step. Plan the first update before launch, because the store is not a finish line: the first month’s usage will disagree with the PRD somewhere, and the second version informed by that is where most apps get good. Platforms move too — Apple’s rule that from April 2027 uploads must be built with the iOS 27 SDK or later is the current example, and iPhone Duo apps: what changes is the current device.