Building React Native, Flutter, and Web SDKs for the Same Product

A few months ago, I thought the difficult part of SDK engineering would be the platform-specific work. Native bridges, packaging, build systems, platform channels, browser APIs. Those were the things I expected to spend most of my time thinking about.

I was wrong.

The hardest part turned out to be making three SDKs feel like the same product.

At Stellon Labs, I helped build and maintain SDKs across React Native, Flutter, and Web. On paper, the goal sounds simple: expose the same capabilities everywhere. In reality, once developers start integrating your SDK, consistency becomes its own engineering problem, and it's usually harder than the implementation itself.

The API Becomes Your Product

Developers don't see your architecture. They don't care how many abstractions sit underneath your SDK. What they experience is the installation process, the documentation, the method names, the examples, the error messages, and the upgrade path. That's the product.

One thing I learned very quickly is that platform parity isn't about copying code across repositories. It's about preserving the same mental model. If a React Native developer understands how a feature works, a Flutter developer shouldn't need to learn an entirely different concept to achieve the same thing.

The implementation can differ. The experience shouldn't.

Three Platforms, Three Different Realities

One thing that becomes obvious when building SDKs is how different these ecosystems really are.

React Native lives somewhere between JavaScript and native mobile platforms. Every bridge, native dependency, permission flow, and build configuration becomes part of the SDK experience. Flutter gives you a more controlled runtime, but plugin development introduces a completely different set of challenges around platform channels and native integrations.

Then there's the web.

Features that feel straightforward on native platforms can suddenly depend on browser security models, storage limitations, user permissions, or runtime differences. A feature might technically exist everywhere, but making it behave consistently is a completely different challenge.

Consistency Is Mostly Process

When people hear "SDK engineering", they usually think about code. Most of the long-term work isn't code at all.

It's asking questions like:

• Are method names identical?
• Are events emitted the same way?
• Are examples updated across every SDK?
• Are release notes synchronized?
• Do all platforms support the same feature set?
• Are error messages understandable?

A surprising amount of engineering time goes into answering those questions. Once developers start depending on your SDK, inconsistency becomes a bug, even when the code works perfectly.

Documentation Finds Problems Faster Than Code Reviews

One habit I've picked up is writing examples early, not after shipping but before shipping.

The quickest way to discover awkward APIs is to build a small application using them. Documentation acts like a stress test. If the quick start guide feels complicated, the SDK is probably complicated. If every example needs paragraphs of explanation, the abstraction is probably wrong.

I've found more API design issues while writing documentation than during implementation. The example app never lies.

The Hidden Cost of Supporting Multiple SDKs

The first release feels exciting. The tenth release feels educational.

Every feature becomes multiple implementations. Every bug report becomes a platform-specific investigation. Every breaking change becomes a coordination problem. Every release requires confidence that all SDKs still behave like one coherent system.

That's where tooling starts mattering. Versioning discipline, shared specifications, automated testing, release workflows, and clear ownership become just as important as the code itself.

Without those systems in place, maintaining multiple SDKs slowly becomes harder than building them.

What I've Enjoyed Most

One thing I didn't expect is how much SDK engineering changes the way you think about products.

You're not building features directly. You're building tools that other developers use to build features. The feedback loop is different, the quality bar is higher, and the responsibility feels different too.

When an SDK is good, developers stop thinking about it. Everything feels obvious. Everything behaves as expected. Ironically, that's usually the result of a huge amount of invisible work.

That's probably my biggest takeaway from working across React Native, Flutter, and Web SDKs.

The goal isn't maintaining three codebases.

The goal is maintaining trust.

Some of the best SDKs I've used felt simple enough that I never thought about them. After helping build them, I don't think simplicity happens by accident anymore.