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GROSSBYTE
$ npx create-expo-app your-app

Mobile appsfrom Hamburg

I build mobile apps for iOS and Android with React Native and Expo – and the backend along with them. One codebase, two platforms, one point of contact.

Start a project
$ ls services/app/

What I do

From the idea to the app in the store – plus everything the app needs behind the scenes.

Apps for iOS & Android

Cross-platform development with React Native and Expo: one TypeScript codebase, native performance and a native look and feel on both platforms.

Backend & API included

Most apps need more than a user interface: accounts, sync, push notifications. I build the backend with AdonisJS and PostgreSQL along with the app.

Builds & app store release

Builds, TestFlight and store submission with EAS – including the stumbling blocks Apple and Google put in your way.

Admin interface & web version

An app often comes with a web back office or a web version. With Nuxt and a shared, type-safe API, app and web share the same data foundation.

Technology consulting

React Native, Flutter, Swift or a PWA after all? I've worked with all of them and help you pick the right technology for your project.

Prototypes & MVPs

Find out quickly whether the idea works: with AI-assisted development, a working prototype takes days instead of months.

$ cat workflow.md

How I work

An app is only done when it's in the store. I'll go the whole way with you.

1. Idea & assessment

We clarify what the app needs to do, who it's for and which platforms matter. You get an honest assessment of effort and technology.

2. Specification & prototype

Requirements become clear tickets, core features become a clickable prototype. That way you see early on whether the app feels right.

3. Development in iterations

App and backend grow together, tested via TestFlight and internal builds on real devices. Feedback goes straight into the next iteration.

4. Release & updates

Store submission, review process and fast updates afterwards – including over-the-air updates for bug fixes without a new store release.

$ cat package.json

Tech stack

  • React Native
  • Expo
  • EAS
  • TypeScript
  • AdonisJS
  • PostgreSQL
  • Nuxt
  • OpenAPI
  • SwiftUI
  • Flutter
  • Ionic
  • Capacitor
  • Firebase
$ man app-development

Frequently asked questions

For most apps, React Native with Expo is the more economical choice: one codebase for iOS and Android, native performance and fast updates. Native development pays off when the app relies heavily on platform features. I've built both and will tell you honestly what fits.
Yes. Builds, TestFlight, store listings and submission to Apple and Google are part of it. You create the developer accounts with Apple and Google – so the app legally belongs to you.
As soon as user accounts, sync between devices or shared data come into play: yes. I build app and backend from a single source so both fit together from the start.
Yes. In our first call we sharpen the idea together and figure out what a first version really needs. A lean prototype is often the best place to start.
No. I'm based in Hamburg, but I work remotely for clients all over Germany and beyond. For clients in and around Hamburg, meeting in person is always an option.
$ grep -r "practice" blog/

From practice

AI06/02/2026

From Flutter through Swift to React Native – how AI lowers the barrier to experimenting

AI doesn't write my code – it lowers the barrier to trying new things. A tech journey through Flutter, Swift and React Native, and why I ended up feeling at home in TypeScript.

8 min
AI05/18/2026

Zutato – ten years of idea, one Saturday evening of website

Last weekend, zutato.com went live. The idea behind it has been with me for almost a decade – the website was done in one Saturday evening. Both are worth talking about.

7 min
Development05/13/2026

Building an app against doom-scrolling – while doom-scrolling

How I built an iOS app against doom-scrolling using pure vibe-coding – and nearly lost my mind in the process. Including AI sleep advice.

10 min

Got an app idea?

A 30-minute call. No sales pitch – just an honest conversation about your idea and how we get it into the store.

Book a call

Write to me directly: moin@grossbyte.io

Response within 24h
Relaxed conversation
No commitment