Write Your First
Compose Screen
in 12 Minutes.
Stop cargo-culting Stack Overflow. KotlinMastery starts with why the code breaks, then shows you how a senior dev would actually write it — in a real production codebase.
Marcus Chen
Lead Instructor · ex-Google
Meet the engineers
who've shipped it.
Every instructor is an active practitioner. No academics. No bootcamp grads teaching what they just learned. People who pull up their own production code.
Marcus Chen
Staff Engineer \u00b7 ex-Google Android
Module
Kotlin Foundations
“Most juniors learn null safety by accident — after the NullPointerException in production. We fix that on day one.”
Priya Nair
Senior Android Engineer \u00b7 Spotify
Module
Coroutines in Depth
“Everyone copies the launch { } snippet. Nobody understands why their coroutine keeps cancelling. We fix that.”
Weather App
Coroutines + Retrofit + StateFlow. A real API call, error handling that doesn't crash, and a Compose UI that reacts to state.
Tomás Herrera
Junior Android Dev → Mid-level
“I'd been writing Kotlin for 8 months and still couldn't explain why my coroutine was leaking. Module 2 fixed that in one afternoon. Got promoted 3 months later.”
GitHub activity after course
Jordan Abara
Principal Engineer \u00b7 Robinhood Mobile
Module
Jetpack Compose
“If you're still thinking in XML when you write Compose, you're carrying the wrong mental model into the new world.”
Sofia Reyes
Android Architect \u00b7 Duolingo
Module
Clean Architecture
“A ViewModel that talks to Retrofit directly isn't an architecture. It's a time bomb. Let me show you the diff.”
Habit Tracker
Room database, Repository pattern, Hilt injection. CRUD that survives rotation, process death, and your QA engineer.
Aisha Okafor
Java dev → Android engineer
“I was writing Kotlin like it was Java with semicolons removed. Marcus's module on data classes and sealed classes rewired how I model state.”
GitHub activity after course
Multi-Module Template
The production scaffold you'll clone for every new job. Feature modules, shared UI, build conventions, and a CI pipeline.
Edit real Kotlin. See it run.
No install. No "Hello World." These are the exact patterns that trip people up in their first production app.
Output
Hit Run to see output
💡 Try This
Try: val userName: String? = "Jordan"
Edit the code. See why ?.let{} beats the null check you've been writing.
No paywalls on the good stuff.
Module 1 is free, no expiration. Pay once for the rest — no subscription, no "access expires in 30 days."
Free
Start learning without a credit card. Module 1 is completely free.
Complete
Every module, every project, lifetime access. The whole course, yours forever.
Team
For engineering teams onboarding to Kotlin or upgrading from Java.
The Kotlin Cheat Sheet
Not a syntax reference. A decision guide — when to use data class vs. sealed class, when coroutines beat threads, how to structure a ViewModel. Two pages. Printable.