Free lesson · Mobile System Design Interviews
Welcome to Mobile System Design
You're about to learn one of the most valuable skills in mobile engineering - the ability to design entire apps from scratch, think through trade-offs like a senior engineer, and communicate your ideas clearly under pressure.
Whether you're preparing for a big tech interview at Google, Meta, or Apple, or you want to grow from a developer who writes features into an engineer who designs systems - this course is for you.
Who Is This Course For?
This course is written for complete beginners to system design. You don't need years of experience. You don't need to have read thick textbooks on distributed systems. If you can build a basic mobile app - even a simple one with a few screens - you have enough background to follow everything here.
That said, even if you're a mid-level or senior developer, you'll find value in the structured thinking patterns, real-world analogies, and the interview-specific strategies we cover.
What Is Mobile System Design, Anyway?
Imagine you walk into an interview and the interviewer says:
"Design Instagram."
That's it. Two words. No requirements doc. No product spec. No Figma mockup.
Your job for the next 45-60 minutes is to figure out what exactly needs to be built, decide how the pieces fit together, and explain your reasoning - all while having a conversation with someone who's evaluating your thinking process.
This is a mobile system design interview. It tests something very different from a coding interview. In a coding interview, there's usually one right answer. In system design, there are dozens of valid approaches. What matters is how you think, not what you build.
Think of it like this: a coding interview is like a math exam - solve the problem, get the answer. A system design interview is like being an architect - there's no single "correct" house, but there are definitely houses that will fall down.
The Building a House Analogy
We'll use this analogy throughout the course because it maps perfectly to how mobile system design works:
The Client (your interviewer) comes to you and says, "I want a house." But they haven't told you how many rooms, whether they need a garage, or if they live in a flood zone. Your first job is to ask the right questions.
The Blueprint (your architecture) is the high-level plan. Where does the kitchen go? How do rooms connect? You're not picking paint colors yet - you're making sure the structure makes sense.
The Foundation & Tools (building blocks) are things like how you store data, how the app talks to the server, how you handle poor network. Every house needs plumbing, wiring, and a foundation. Every app needs networking, storage, and a solid architecture.
The Construction (deep dives) is where you actually dig into specific challenges. How do you make the scrolling smooth? What happens when the user goes offline? How do you handle real-time updates?
The Walkthrough (wrap-up) is your final tour with the client. You summarize what you built, acknowledge what you would improve with more time, and show you understand the trade-offs.
This is exactly the 5-step framework we'll teach you in Module 2, and every single case study in this course follows these steps.
How This Course Is Structured
We've organized everything into a deliberate learning path. Here's the roadmap:
Module 1: Welcome (You Are Here)
A quick orientation to set you up for success.
Module 2: The 5-Step Interview Framework
Before we design anything, you'll learn the repeatable framework that works for ANY mobile system design question. Each of the 5 steps gets its own dedicated lesson so you understand not just "what" to do, but "why" and "how." By the end of this module, you'll have a mental playbook you can apply to any question - even ones you've never seen before.
Module 3: The Toolbox - Building Blocks
This is like learning your tools before you start cooking. Each topic - architecture patterns, data storage, networking, caching, push notifications, and more - gets its own focused lesson. When you hit the case studies, you'll already know these pieces. You'll just be combining them in different ways.
Modules 4-11: Case Studies
This is the core of the course. Eight real-world app designs, ordered from simpler to more complex:
- Social Feed App - The classic. Infinite scrolling, offline caching, rich content rendering.
- Chat Application - Real-time messaging, delivery receipts, message ordering.
- Video Streaming App - Adaptive playback, prefetching, bandwidth management.
- Hotel Booking App - Search, filters, reservation holds, payment flow.
- Real-Time Financial App - Live charts, data accuracy, low-latency updates.
- Cloud Storage App - File sync, uploads, version history, encryption.
- Pagination Library - Something different - designing a reusable library, not an app.
- Ride-Sharing App - Real-time location, maps, driver-rider matching.
Each case study is split into multiple focused topics:
- Problem & Discovery - What are we building? What questions should you ask?
- API Design - How does the app talk to the backend?
- Architecture - What's the high-level blueprint?
- Deep Dives - The hard problems that make this app unique.
- Summary & Variations - Wrap-up, key takeaways, and "what if" variations.
Module 12: Cheat Sheets & Quick Reference
A distilled set of reference cards you can review the night before your interview.
What Makes Our Approach Different?
Foundations first. Most courses throw you into case studies immediately. We don't. By the time you hit your first case study, you'll already understand architecture patterns, networking trade-offs, and storage options. The case studies become about combining pieces you already know, not learning everything at once.
Each case study builds on the last. We've ordered them intentionally. The Social Feed teaches you offline caching - then the Chat App extends that with message queues. The Video App introduces streaming - then the Financial App shows you real-time data at an even faster pace. By Case Study 5, you'll notice you're reusing patterns from earlier studies. That's the point.
Beginner-friendly language. No concept is introduced without an analogy or a "think of it like..." explanation. We use everyday comparisons - restaurants, postal services, libraries - to make abstract ideas stick.
The interviewer's perspective. Throughout every case study, we include sidebars that tell you what the interviewer is actually thinking at each stage. Knowing what they're evaluating helps you emphasize the right things.
Practice variations. Each case study ends with "what if" questions - alternative versions of the same problem that teach you to think flexibly, not memorize answers.
Both platforms covered. Where code examples appear, we show both Kotlin (Android) and Swift (iOS) side by side, so you can follow along regardless of your platform.
How to Get the Most Out of This Course
Here are a few tips based on how people actually learn system design:
Read Module 2 first, no matter what. The 5-step framework is the backbone of everything. Skipping it is like trying to cook without knowing how to turn on the stove.
Don't skip Module 3 (The Toolbox). It's tempting to jump to the case studies. Resist. The toolbox module is what separates "I sort of understand this" from "I can confidently explain my choices."
After each case study, close the material and try it yourself. Open a blank document, pretend you just heard the question in an interview, and try to walk through the 5 steps from memory. This is the single most effective study technique for system design.
Talk out loud. System design interviews are conversations. Practice explaining your thinking out loud, even if you're alone. If a concept feels clear in your head but you can't explain it simply, you don't understand it well enough yet.
Don't memorize - understand. If someone asks you "why WebSockets for a chat app?" you shouldn't recite a definition. You should be able to explain it like you're telling a friend: "Imagine you're on the phone with someone. HTTP is like hanging up after every sentence and calling back. WebSockets is like keeping the line open so you can both talk freely."
What You'll Be Able to Do After This Course
By the end, you'll be able to:
- Walk into any mobile system design interview with a clear, repeatable framework.
- Break down any app - even ones you've never used - into its core components.
- Make architecture decisions and explain the trade-offs behind them.
- Design APIs that make sense for mobile clients.
- Handle deep-dive questions about offline support, real-time data, performance, and more.
- Communicate your design clearly and confidently, like someone who builds systems for a living.
Let's get started.