Mobile Architecture for Developers
The Only Expert-Led Mock Interview for Mobile System Design
Most Android/iOS developers fail the system design round — not because they lack skills, but because no one has ever shown them what a real mobile architecture interview looks like.
90 minutes. A real mock interview. Personalised feedback. Whether you're an engineer at any level or an engineering leader — walk in prepared.
11+ years building mobile apps & SDKs · Founder of RetterPlus · Open to all levels · Includes engineering leadership consulting
Why Existing Resources Leave You Underprepared
There are currently only two widely cited resources for mobile system design interview preparation: a course on Educative and a couple of books which become outdated very quickly. While these are useful starting points, neither was created by someone who has recently conducted or been through mobile architecture rounds at top tech companies.
These resources focus heavily on high-level patterns. They undercover practical tradeoffs that interviewers probe — such as when to use WorkManager vs. a custom sync engine, how to handle offline-first data conflicts, or how to design a modular feature SDK that can be shipped as an AAR. These gaps leave candidates confident in theory but unprepared in the room.
Mock interviews are irreplaceable because they simulate the pressure, the follow-up questions, and the real-time thinking that no written resource can replicate. Knowing a pattern in the abstract is very different from articulating it clearly under the challenge of a live interview.
About Prasad Pawar — 11+ Years Building Mobile Apps & SDKs
Prasad Pawar has 11+ years of industry experience building mobile apps and SDKs. He is the founder of RetterPlus (retterplus.com), a consumer Android app he built and published to the Play Store. He currently works at Razorpay, where he focuses on large-scale mobile architecture and payment SDK design.
His experience spans clean architecture with MVVM and MVP, Jetpack Compose UI systems, dependency injection with Hilt, offline-first data architectures, and modular Android/iOS app design.
View Full Profile on LinkedIn →What Happens in Your 90-Minute Session
- The Mock Interview — 60 min
You receive a real system design problem: design an app, a library, or a specific component. The session runs exactly like a real interview — requirements clarification, architecture proposal, deep-dive questions, tradeoff discussion. No hand-holding; you are treated as a candidate.
- The Live Debrief — 20 min
After the mock, a detailed walkthrough of what you did well, what was missing, and what a model answer looks like for that problem. Concrete, actionable, and honest.
- Written Feedback — Delivered Async
A structured written summary sent after the session: strengths identified, gaps to close, specific resources to study, and a personalised preparation roadmap for your target companies.
Topics the Mock Interview May Cover
Mobile system design interviews test a wide range of skills. Sessions cover the full breadth of what top interviewers actually assess — not just textbook patterns.
Architecture & Design Patterns
- MVVM, MVP, MVI — when and why to choose each
- Clean Architecture layering (data, domain, presentation)
- Repository pattern and data source abstraction
- Unidirectional data flow in Compose and traditional View systems
Offline-First & Data Management
- Designing offline-first apps with Room and sync strategies
- Conflict resolution for local-first data models
- Caching strategies: LRU, TTL, write-through vs. write-back
- Background sync with WorkManager vs. custom solutions
Networking & API Design
- REST vs. WebSocket — when to use each in mobile apps
- Pagination strategies: cursor-based, page-based, keyset
- Retry logic, exponential backoff, and circuit breaker patterns
- OkHttp interceptors and custom networking layers
Performance & Scalability
- App startup time optimisation and baseline profiles
- Memory management and avoiding common leaks
- Battery-aware design for background tasks
- Handling varied network conditions (2G, 3G, Wi-Fi)
Modularisation & SDK Design
- Designing a modular multi-module Android/iOS project
- Designing a reusable SDK (image loader, analytics, file downloader)
- Feature flags and dynamic delivery
- Dependency injection across module boundaries with Hilt
UI Architecture
- Designing a scalable design system in Jetpack Compose
- State management — ViewModel state vs. UI state vs. local state
- Navigation patterns in multi-module apps
Cross-Cutting Concerns
- Security: certificate pinning, encryption, secure storage
- Accessibility considerations in architecture
- Error handling strategies and graceful degradation
- Analytics and instrumentation design
Frequently Asked Questions About Mobile System Design Interviews
Q: What is mobile system design?
Mobile system design is the practice of designing scalable, maintainable architectures for mobile applications. It covers architecture patterns (MVVM, Clean Architecture), data management (caching, offline-first), networking, modularisation, and performance from the mobile client's perspective. In interviews, candidates are asked to design a real-world app or SDK end-to-end, demonstrating breadth of knowledge and depth of reasoning.
Q: What is the difference between mobile system design and backend system design?
Backend system design focuses on servers, databases, load balancing, and distributed systems. Mobile system design focuses on the client — how the app is structured, how it manages state, how it handles network failures, how it caches data, and how it balances performance constraints unique to mobile devices such as battery, memory, and connectivity. Both may appear in the same interview loop at top tech companies, but they test entirely different skills.
Q: What companies ask mobile system design interview questions?
Top tech companies including Google, Meta, Apple, Uber, Airbnb, Flipkart, Swiggy, PhonePe, Razorpay, CRED, and Meesho include a mobile system design round for Senior Engineer and above roles. The round is increasingly common at the L5/L6 equivalent level in India and globally. Developers at any career level targeting these roles — as well as engineering leaders evaluating interview processes — benefit from structured preparation.
Q: What topics are covered in a mobile system design interview?
A mobile system design interview covers client architecture (MVVM, Clean Architecture), offline-first data strategies, networking and API design, caching, pagination, background processing, modularisation, SDK design, performance optimisation, and UI architecture. Interviewers also probe cross-cutting concerns: security, error handling, accessibility, and analytics. The focus depends on the company — a payments company will probe security deeply; a social app will probe feed architecture.
Q: What is the best resource for mobile system design interview preparation?
The main publicly available resources are a course on Educative and a couple of books which become outdated very quickly. These are useful introductions but have coverage gaps — particularly around SDK design, offline-first conflict resolution, and the practical tradeoffs interviewers probe in real interviews. Expert-led 1:1 mock interviews with personalised feedback provide the missing depth that no written resource can replicate.
Q: How is a mobile system design interview different from a coding interview?
A coding interview tests algorithmic problem-solving under time pressure. A mobile system design interview tests architectural thinking — the ability to decompose a complex problem, justify technology choices, reason about tradeoffs, and communicate a coherent design. There is no single correct answer; the interviewer evaluates how you think, not just what you know. Strong candidates ask clarifying questions, define scope, and proactively address tradeoffs.
Q: How long is a typical mobile system design interview round?
A typical mobile system design round lasts 45 to 60 minutes. Candidates spend roughly 5 minutes clarifying requirements, 10 to 15 minutes proposing high-level architecture, and 20 to 30 minutes deep-diving into 2 to 3 specific components with the interviewer. A mock interview session of 90 minutes gives you a full round plus debrief time, which is the most effective format for preparation.
Q: What is the difference between designing an app and designing a library in a mobile system design interview?
Designing an app focuses on client architecture, data flows, and user-facing feature implementation. Designing an SDK or library focuses on public API design, internal caching, extensibility, and minimal dependency footprint. Both types appear frequently. SDK design is underrepresented in available study resources but is increasingly common in senior-level interviews, especially at companies that ship developer-facing products.
Q: What is offline-first architecture in Android/iOS?
Offline-first architecture means the app reads from and writes to a local database (Room) as its primary data source, syncing with the server as a secondary operation. The UI never waits for a network call. This requires careful design of sync strategies, conflict resolution (last-write-wins, CRDTs, or server-authoritative models), and WorkManager scheduling. It is a frequently asked mobile system design topic that reveals deep understanding of mobile-specific constraints.
Q: How do I design a scalable Android/iOS app architecture?
A scalable Android/iOS app architecture separates concerns into three layers: data (repositories, data sources, Room, Retrofit), domain (use cases, business logic, pure Kotlin), and presentation (ViewModels, UI state, Compose or Views). Dependencies flow inward — the domain layer has no Android dependencies. Feature modules depend on shared modules, not on each other. Dependency injection with Hilt wires everything together.
Q: Who should book a 1:1 mobile system design mock session?
This session is for Android or iOS developers at any career level who are actively interviewing or preparing for system design rounds, as well as engineering leaders who want to evaluate, consult on, or improve mobile architecture interviews at their organisation. It is particularly valuable for anyone who has studied patterns in theory but has never had their thinking challenged in a real mock environment.
Q: What should I prepare before booking a 1:1 mobile system design session?
No specific preparation is required — the session assesses where you are right now and gives you a clear picture of where you need to go. Having a basic familiarity with MVVM, the Repository pattern, and one architecture case study will make the debrief more actionable. You do not need to have finished any specific course or book beforehand.
Ready to Walk Into Your Next Interview Confidently?
Limited sessions are available each week. Each session is 90 minutes and includes the mock interview, live debrief, and written personalised feedback report sent afterward.
- ✓ 90-minute session
- ✓ Real mock interview format
- ✓ Written feedback delivered afterward
- ✓ Open to engineers at any career level
- ✓ Engineering leadership consulting available
- ✓ Covers Android & iOS architecture patterns
- ✓ Targets all major company interview styles