About Mobile Design Rounds

Mobile system design interviews test how you build the client side of an app: storage, networking, background work, offline behavior and failure handling. Most prep material is written for backend engineers. This site covers the mobile version, for Android and iOS engineers.

Who writes it

An independent Android developer. The author is not named on this site, so judge the work by its sources: every case study ends with a dated note on what was verified and what was not, with links to the official documentation it relies on.

How the case studies are made

Drafts are written with AI assistance. Every technical claim is then checked against official documentation: the Android developer site for Android and Apple's developer documentation for iOS. Kotlin snippets are compiled and Swift snippets are type-checked, with stand-ins only for app-specific placeholder types. Each case study ends with a note listing what was verified, on what date, and what could not be verified. Where the official guidance is silent, the text says so.

The Android sections follow the official architecture guidance. The iOS sections are written by an Android developer from Apple's documentation, so treat them as a careful second opinion, and tell me if something is wrong.

Corrections and requests

Found a mistake, or want a case study on a specific app? Open an issue on GitHub. Corrections are credited and fixed quickly. You can also follow new case studies with the RSS feed.

This site is independent and is not affiliated with Google, Apple, or any company named in a case study. Android, iOS, Swift and Kotlin are trademarks of their respective owners.