TL;DR: Modern app development offers multiple approaches for building across platforms. This guide explains Kotlin, Kotlin Multiplatform, and Compose Multiplatform. Understanding these distinctions helps you make informed decisions about which approach best fits your project’s needs.
Navigating modern app development with Kotlin
Businesses today want efficient ways to build great apps for all their users—whether they’re using iPhones, Android phones, desktop computers, or web browsers. The tech world offers many solutions, often accompanied by confusing buzzwords and competing claims.
You’ve likely heard of Kotlin, a modern programming language making waves, especially in Android development. But Kotlin’s capabilities extend beyond Android, offering powerful ways to build applications for multiple platforms. Understanding terms like “KMP“ and “Compose“ is key to making wise technology choices for your projects.
This article is your straightforward guide. We’ll explain Kotlin and then explore two of its powerful multiplatform approaches: Kotlin Multiplatform (KMP) and Compose Multiplatform. We’ll clarify the differences and illustrate with examples when each approach makes sense, drawing on insights from development experts who work with these technologies daily.
What is Kotlin? The language that powers modern apps
Kotlin is a modern, versatile programming language created by JetBrains, the company behind many popular developer tools. Think of it as an evolution of older programming languages, designed to be more concise, safer to use, and more enjoyable for developers than predecessors like Java.
Kotlin gained massive popularity in the Android world when Google officially named it a preferred language for Android app development. This means millions of Android apps today benefit from Kotlin’s efficiency and reliability. Developers appreciate that Kotlin often accomplishes the same tasks with significantly less code while helping prevent common programming errors that can cause apps to crash.
Understanding Kotlin as a powerful and flexible language foundation is the first step to understanding its multiplatform capabilities. The language’s design makes it well-suited not just for Android development, but for building applications that work across different types of devices and operating systems.
Kotlin Multiplatform (KMP) for core logic
Kotlin Multiplatform, often abbreviated as KMP, is a feature of the Kotlin language that lets developers write standard, behind-the-scenes code once and share it across different platforms like iOS and Android. This shared portion is typically the app’s “brain“—its core business logic, how it handles data, and how it communicates with servers.
How KMP works
As Lead Developer Scott Keller explains, KMP is effective because it “actually cross-compiles your shared Kotlin code to the specified native target. This means the shared logic runs efficiently as part of the native application.”
Think of it like translating a book into different languages. KMP takes your Kotlin code and translates it into the “native language” that each platform speaks best:
- For iPhones and iPads, it creates code that iOS apps can use directly.
- For Android devices, it speaks Android’s language.
- For web browsers, it converts to JavaScript (the language of the web).
- For other platforms, it adapts accordingly.
This smart translation process means your app runs at full speed on each device, just as if it were written specifically for that platform. There’s no performance penalty or extra layer slowing things down; the shared code becomes a natural part of each app.
What about the user interface?
Crucially, with the KMP approach for sharing logic, the user interface, what users see and touch, remains 100% native to each device. Your iPhone app interface is built with Apple’s tools, like Swift and SwiftUI, and your Android app interface uses Google’s tools. They simply share the same reliable “brain“ underneath.
When to consider KMP
This approach typically makes sense when you need the absolute best, pixel-perfect native look and feel on each device, have existing native apps you don’t want to rebuild, or require complex business rules that must be identical across platforms for accuracy or compliance.
As Scott Keller explains, the big win is in maintenance and evolution: “If a bug is found or the logic of how some functionality works needs to change, we can do it in one place.”
This eliminates the complexity of managing separate tickets, platform-specific implementations, and coordinating rollouts across multiple teams. You maintain your existing native development expertise and UI investments while dramatically reducing the effort needed to keep business logic synchronized across platforms.
Compose Multiplatform for UI
What if you want a highly consistent visual design and user experience for your app, not just on phones but also on desktop computers or the web? That’s where Compose Multiplatform comes in. It’s a modern toolkit from JetBrains, developed in partnership with Google’s Compose team. It lets developers use Kotlin to design and build the app’s user interface once and then deploy that same interface across many different platforms.
Logic sharing included
Naturally, the “brain“ behind this shared UI, the business logic, can also be written in Kotlin and shared using the KMP principles discussed earlier. This means Compose Multiplatform projects often share both the interface and the underlying logic. iOS support reached stable status in 2024, making Compose Multiplatform a viable option for production applications across all major platforms. Notably, Compose’s Skia-based rendering on iOS delivers performance on par with SwiftUI, ensuring smooth and responsive experiences for iPhone and iPad users.
Flexibility within shared UI
Compose Multiplatform offers flexibility even within its shared approach. For example, an application built primarily with shared UI components can still incorporate platform-specific elements when they provide superior functionality. A mobile app might use a native iOS map component within its otherwise shared interface to ensure the best possible mapping experience for iPhone users.
The opposite is equally true: existing native applications can incorporate Compose Multiplatform screens or components wherever it makes sense. This means you’re not locked into an all-or-nothing approach.
Teams can start with just one shared feature or screen, test how it works for their needs, and gradually expand usage over time. This flexibility makes it practical for real-world projects where incremental adoption often works better than complete rewrites.
When to consider Compose Multiplatform
This approach typically works well when:
- You’re building a brand-new application and want a highly consistent look and feel across all target platforms.
- Your team has strong Kotlin skills or wants to build full-stack expertise in one language.
- Speed to market with a consistent interface across many different types of devices is a high priority.
- Brand consistency and unified user experience across platforms outweigh platform-specific interface optimizations.
- Your Android team is already experienced with Kotlin and Jetpack Compose, making the transition to Compose Multiplatform more straightforward than learning entirely new frameworks.
Real-world examples
Who’s using KMP for shared logic
Major companies are already using Kotlin Multiplatform in production to share business logic while keeping native user interfaces:
- McDonald’s shares core functionality across its mobile apps, reducing development time while maintaining platform-perfect experiences.
- Cash App leverages KMP to ensure financial calculations and business rules work identically on iOS and Android.
- Netflix Studio uses KMP to power its internal production tools across platforms
- Forbes shares over 80% of their business logic, allowing them to “roll out new features simultaneously on both platforms with a small fraction of the engineering effort.”
- Google Workspace is migrating from its in-house solution to KMP for apps like Docs, Sheets, and Slides.
These companies chose KMP because they wanted to eliminate duplicate business logic while keeping their iOS apps feeling like iOS and their Android apps feeling like Android.
Who’s exploring Compose Multiplatform for shared UI
Compose Multiplatform, with iOS support reaching stability in 2024, is newer but gaining adoption for projects where consistent interfaces matter:
- JetBrains’ development tools showcase the approach with unified interfaces across desktop platforms
- Internal enterprise applications where employees use the same tools on phones, tablets, and computers
- New startups and greenfield projects that prioritize speed to market and brand consistency over platform-specific design
The key difference is that KMP users share the “brain” (logic) while keeping native “faces” (UI), while Compose Multiplatform shares both for complete consistency across platforms.
Key differences & making wise choices
Understanding the distinctions between these approaches helps clarify your options:
- Kotlin: The modern programming language that serves as the foundation for both approaches.
- KMP (for logic with native UI): Uses Kotlin to share only the non-UI core logic. User interfaces are built natively for each platform using platform-specific tools and following platform-specific design guidelines.
- Compose Multiplatform (for UI and logic): Uses Kotlin to share both the user interface and the core logic across platforms, creating consistent experiences everywhere.
It’s about the right tool for the job.
Neither approach is universally “better.“ The best choice depends entirely on your project’s specific goals, your priorities for user experience (unique native feel versus cross-platform consistency), your team’s existing skills, and your long-term vision for the application.
Understanding the complexities
Because these are advanced, evolving technologies, understanding these distinctions is essential for making informed decisions. Like many powerful development tools, initial setup and configuration require expertise to optimize properly. Even with powerful sharing capabilities, a small portion of an app (around 10%) often needs platform-specific code for unique device features or optimal integration. Kotlin provides elegant ways to handle this through features like its expect/actual mechanism, but it highlights the importance of expert architectural planning when implementing multiplatform strategies.
Making informed decisions for your projects
Kotlin offers a robust language foundation with multiple paths for multiplatform development. Kotlin Multiplatform (KMP) provides a strategic way to share your app’s “brain“ while keeping its “face“ native to each platform. Compose Multiplatform offers a path to share both the “brain“ and the “face“ for consistent experiences everywhere.
Understanding these core concepts—Kotlin as the language, KMP for logic sharing, and Compose for UI sharing—equips you to have more informed conversations with your development teams or technology partners about the best approach for building your next application.
The choice between these approaches depends on factors like your user experience priorities, existing codebase, team capabilities, target platforms, and long-term maintenance considerations. Each approach offers distinct advantages when applied to the right scenarios.
Originally published on https://www.inspiringapps.com.
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