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Cross-platform app development for iOS and Android from one codebase
Cross-platform app development means building one app, from one shared codebase, that ships to both the App Store and Google Play. We build with Flutter, React Native and Kotlin Multiplatform for startups, product companies and healthcare organizations. We help you pick the framework that fits your team, and we write native code where the platform demands it.
What we build with one shared codebase
Three frameworks, each with a different idea of what to share. We pick the one that matches your product, your team and the native features you need.
Flutter apps
Flutter apps are written in Dart. Flutter ships its own widget set instead of using the system controls, renders it with the Impeller engine, and compiles release builds to machine code. You get one UI that looks the same on iOS and Android, with Material and Cupertino widgets when you want a platform feel. Native features are reached through platform channels or Pigeon-generated, type-safe interfaces, with host code in Swift or Kotlin. We cover the app with unit, widget and integration tests, and the same codebase can later target web and desktop.
Dart · Impeller rendering · Platform channels & Pigeon · Widget & integration tests
React Native apps
React Native apps are written in TypeScript with React, and the components are backed by real Android and iOS views at runtime. That makes it a strong fit when your team already builds the web product in React. When a library does not cover a platform API, we write a Turbo Native Module: a TypeScript spec, Codegen interfaces, and native code in Kotlin on Android and Objective-C++ on iOS. Testing runs from Jest unit tests and React Native Testing Library component tests to end-to-end flows on real devices with Detox or Maestro.
TypeScript & React · Turbo Native Modules · Codegen · Jest & E2E tests
Kotlin Multiplatform
Kotlin Multiplatform shares logic, not necessarily the UI. Business rules, networking, validation and the data layer live once in Kotlin common code, and platform source sets hold the parts that need iOS or Android APIs. The screens can stay fully native in SwiftUI or UIKit and Jetpack Compose, so each app keeps its platform look and behavior. If you want shared screens too, Compose Multiplatform is stable on Android, iOS and desktop. KMP also suits teams that want to add shared code to existing native apps one module at a time.
Shared Kotlin logic · SwiftUI & Jetpack Compose · Compose Multiplatform · Incremental adoption
Healthcare & mHealth apps on one codebase
Health apps need native access, and cross-platform frameworks handle it through bridges. We read and write HealthKit data on iOS and Health Connect data on Android through native modules or platform channels, requesting only the data types each feature uses. On Google Play that means a Health apps declaration with a justification per data type; Apple bars using HealthKit data for advertising and storing personal health information in iCloud. We add Bluetooth device pairing, secure storage in Keychain and Keystore, and design the app with HIPAA safeguards when it handles PHI.
HealthKit · Health Connect · Per-type permissions · HIPAA safeguards
MVPs & multi-platform products
One codebase lets an MVP reach both app stores without building the product twice. When the product needs more surfaces, the framework choice matters: Flutter supports web, Windows, macOS and Linux targets from the same project; React Native reaches Windows and macOS through Microsoft-maintained platforms and the web through the community React Native Web project; Kotlin Multiplatform shares logic with desktop and web targets, with Kotlin/Wasm web still in Beta. We structure the MVP so the shared core, API contracts and design system carry into version two instead of being thrown away.
App Store & Google Play · Web & desktop targets · Shared design system · Built to scale past MVP
What goes into a cross-platform app
The shared code is only part of the work. These six building blocks decide whether one codebase stays easy to ship on two platforms.
Framework choice & architecture
We compare Flutter, React Native and Kotlin Multiplatform against your team's skills, the native APIs you need and your web plans. Then we set the module boundaries: what is shared, what stays platform-specific, and how state, navigation and errors flow through the app.
Shared UI & design system
One component library with tokens for color, type and spacing, built in the framework's own widgets or components. We respect platform conventions where users expect them, such as back navigation, date pickers and system sheets, and support dynamic type and screen readers on both platforms.
Learn moreNative modules & platform channels
When the framework or its libraries do not expose an API, we write the native side ourselves in Swift, Kotlin or Objective-C++. Typical cases are HealthKit, Health Connect, Bluetooth devices, background tasks, biometrics and secure storage, each wrapped behind a typed interface the shared code calls.
Offline data & sync
A local database keeps the app usable without a connection, and a sync layer resolves changes when it comes back. We define which data is cached, how long it lives on the device, how conflicts are handled and how sensitive records are encrypted at rest.
Backend & API integration
Most apps are only as good as the API behind them. We design or connect REST and GraphQL APIs, authentication with OAuth 2.0 and OpenID Connect, push notifications through APNs and Firebase Cloud Messaging, and, for healthcare, FHIR endpoints of EHR systems.
Learn moreCI/CD & store releases
Automated pipelines build, test and sign both apps on every change, then deliver them to TestFlight and Google Play testing tracks. We manage certificates, provisioning, store listings, privacy labels and the Data safety form, so releases stay routine instead of a two-day ordeal.
Learn moreNative vs. cross-platform
Two native apps or one shared codebase?
Two native apps give you full access to each platform and its newest features on day one, and they are the better pick for graphics-heavy, deeply platform-integrated or watch-first products. Cross-platform makes sense when most of the app is shared logic and standard screens, and you want one team shipping both stores in step. Many products land in between, with Kotlin Multiplatform sharing logic under native UI.
Feature parity on iOS and Android
Off-the-Shelf
Two codebases implement each feature separately; parity depends on coordinating two teams or two workstreams.
Custom-Built with Woltrio
Most features are written once and released to both stores together, with platform code only where needed.
Newest OS features and APIs
Off-the-Shelf
Available from day one in Swift and Kotlin, with Apple's and Google's own tools and samples.
Custom-Built with Woltrio
Reachable through native modules or platform channels; framework libraries may need time to catch up.
Graphics-heavy or deeply integrated apps
Off-the-Shelf
The better choice for AR, advanced camera work, widgets, watch apps and heavy background processing.
Custom-Built with Woltrio
Works well for forms, lists, dashboards and media; specialist features become native modules inside the app.
Team and hiring
Off-the-Shelf
Needs Swift and Kotlin skills, usually two specialists or more for each platform.
Custom-Built with Woltrio
One team in Dart, TypeScript or Kotlin, plus native skills for bridges and store tooling.
Long-term maintenance
Off-the-Shelf
Two codebases to upgrade, but no dependency on a framework's release cycle.
Custom-Built with Woltrio
One shared codebase to maintain, plus framework upgrades to plan alongside yearly OS changes.
If native is the right answer for your product, we will tell you and build it that way.
Built for both stores and real users
Security, integrations, offline use and insight, handled the same way on iOS and Android.
Tokens and keys live in Keychain and Android Keystore, never in plain storage. We add biometric unlock, session timeouts and TLS everywhere. Our development work runs under an ISMS that is ISO/IEC 27001:2022 certified, and health apps are designed with HIPAA safeguards.
How we approach cross-platform projects
We are framework-neutral and healthcare-first. The goal is the app that is easiest to ship and maintain for your situation, not the one we prefer to write.
An honest framework recommendation
We map your features to native APIs before choosing a framework, and we say so when two native apps or Kotlin Multiplatform with native UI is the better fit. The decision and its trade-offs are written down, so your team can revisit it later.
Native skills behind the shared code
Cross-platform apps still meet Xcode, Gradle, signing and platform APIs. Our engineers write the Swift and Kotlin side themselves, so a missing library or a new OS requirement does not stall the project or force a workaround.
Health data handled with care
We plan permissions, consent, data minimization and store declarations from the first sprint. We sign a Business Associate Agreement (BAA) with healthcare clients before PHI is shared, and we build systems designed to support HIPAA compliance.
From idea to both app stores
- 01
Discovery & framework choice
We list the features, native APIs, devices and integrations you need, check them against each framework, and recommend Flutter, React Native, Kotlin Multiplatform or native, with the reasons written down.
- 02
UX design & prototype
Flows and screens are designed once with iOS and Android conventions in mind, then tested as a clickable prototype with real users, so open questions are settled before development starts.
- 03
Build in sprints
Shared code and native modules are built in two-week sprints. Every sprint ends with test builds on iOS and Android devices that you can install through TestFlight and Google Play testing tracks.
- 04
Test & submit
Automated unit, widget or component and end-to-end tests run on both platforms. We prepare store listings, privacy labels, the Data safety form and any health declarations, then submit for review.
- 05
Release & maintain
After launch we monitor crashes and performance, keep up with yearly OS releases and store policy changes, and plan framework upgrades so the shared codebase never falls far behind.
Frequently
Asked Questions
Seeking basic information? Our FAQ section is a ready reckoner with precise answers to the most probable queries.
What is cross-platform app development?
Flutter, React Native or Kotlin Multiplatform: which should we choose?
When is native development the better choice?
Can a cross-platform app use HealthKit and Health Connect?
Can we update the app without going through app store review?
Is a cross-platform app slower than a native app?
How do you test a cross-platform app on both iOS and Android?
How do you protect health data in a mobile app?
Sources & Standards
- App Review Guidelines (developer.apple.com)
- Device and Network Abuse policy, Play Console Help (support.google.com)
- Publish your health app on Google Play (developer.android.com)
- Writing custom platform-specific code (docs.flutter.dev)
- Turbo Native Modules (reactnative.dev)
- Kotlin Multiplatform supported platforms (kotlinlang.org)
- Health Breach Notification Rule (ftc.gov)
Keep exploring
Related pages.
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