Mobile apps that work the same on every screen
In short
What is API-first mobile app development?
API-first mobile app development means writing the contract between the app and the server before building either. Onpolar defines one OpenAPI specification, generates typed clients from it and builds the iOS, Android and web apps and the backend against that single document, so they cannot drift apart as the product changes.
- Platforms
- iOS · Android · web
- Typical timeline
- 8–14 weeks to the app stores
- Backend
- Go · PostgreSQL · OpenAPI
Updated
How it fits
One contract, every app
How an API-first app comes together, week by week.
- Weeks 1–2The contractEndpoints, data and errors agreed in one OpenAPI document.
- Weeks 3–5The backendGo and PostgreSQL with the logins, roles and data the app needs.
- Weeks 3–5Typed clientsGenerated from the contract, so a breaking change fails the build.
- Weeks 6–11The appScreens, offline mode, push and sign-in for iOS and Android.
- Weeks 12–14In the storesSigned, reviewed and rolled out to users in stages.
What you get
iOS and Android from one codebase
Cross-platform where the app is screens over data, native where a feature needs it.
The backend and API
Logins, roles and data built on one contract, not an app waiting for an API.
Push, offline and sign-in
Notifications that arrive, an app that copes with a bad connection, biometric login.
Store releases
Signing, staged rollout and crash reporting, all in your own developer accounts.
How it works
- 01
Contract
What the app does, agreed as one API document before any screen is designed.
- 02
Build
Backend, generated clients and the app built against that one contract.
- 03
Release
Submitted to the App Store and Google Play, then improved release by release.
Compared
One cross-platform app vs two native apps
| Compared on | Cross-platform app | Two native apps |
|---|---|---|
| Codebases | One | Two |
| Releases | One, for both stores | Two, often out of step |
| Best for | Business apps: screens over data | Camera, sensors or heavy graphics |
| A change costs | One change | Two changes |
Questions
Have you shipped mobile apps before?
Onpolar’s published case studies are web platforms and SaaS, so the honest answer is that our mobile evidence is the API layer rather than an app store listing. ERPFlow was built API-first on one OpenAPI contract so web, mobile and AI clients can share it. If an app in our portfolio is your bar, say so early and we will tell you plainly.
Should we build native or cross-platform?
Cross-platform, unless the product is really about the camera, sensors, background processing or frame rate. Most business apps are screens over data, and maintaining two codebases for that costs twice as much for no return. Onpolar recommends native only when a feature genuinely needs it.
Do we even need a mobile app?
Often not. With no push notifications, no offline use and no device features in play, a fast web app reaches more people for less money and skips the store review queue. Onpolar would rather talk you out of an app than build one nobody installs.
Who owns the app store accounts and the code?
You do, in your name, from the start: the App Store and Google Play listings, the signing certificates and the repository. Apps held inside an agency’s account are a well-known way to lose control of a product.
Can you build an app on our existing backend?
Yes. The first step is writing the contract for what already exists. If there is no specification, Onpolar produces one from the running API and checks it against real responses, because an app built on a guessed API breaks without warning.