Mobile system design interviews · Android + iOS
What happens when the network drops?
That is the question behind every mobile system design round. Our case studies answer it step by step for Android and iOS, with the code and every failure mode.
New case studies appear in the feed first. Any RSS reader works.
Try it: send a message on a bad connection
The design from the chat case study, running live.
Chat screen
On the device
Outbox
Server
Duplicates ignored: 0
A round is a time budget
Most candidates spend it drawing boxes. The strongest answers save the largest block for the hard part and finish with failure and rollout.
- Requirements5 min
- API and data model8 min
- Client architecture10 min
- The hard part17 min
- Failure, offline, rollout5 min
Case studies
Depth over breadth: fewer designs, each taken all the way through.
- Design a chat appOutbox, idempotent sends, WebSocket and push sync.Read now
- Design a news feedPagination, optimistic writes, cache invalidation.Read now
- Design photo backup and file syncResumable uploads, block-level sync, conflicts.Read now
- Design a pagination libraryLibrary API, generics, request prioritization.Read now
- Design an image loading libraryMemory and disk caches, decoding, cancellation.Read now
- Design a hotel or ride booking appHolds, time sync, payments, search.Read now
- Design a stock ticker appStreaming updates, buffered UI, always-online.Read now
- Design a video streaming appPrefetching, adaptive bitrate, playback state.Read now
- Design an analytics SDKBatching, persistence, privacy, versioning.Read now
- Design a push notification SDKToken lifecycle, delivery, deep links.Read now
Guides
Cross-cutting guides that tie the case studies together.
- Staff-level mobile system design: what the round testsHow staff answers differ from senior ones, what interviewers can observe, and a four-week practice plan.Read now
- Offline-first mobile system design: one model, five case studiesThe official offline-first model applied to chat, feed, upload, booking, analytics and push.Read now
One design, every failure mode
Process death, lost acks, duplicate pushes, clock skew. Each case study lists what breaks and the fix.
Android and iOS, side by side
The architecture is shared. We show where Room becomes SwiftData, and where WorkManager has no iOS equivalent.
What to say at each level
Mid, senior and staff answers spelled out, plus the follow-up questions interviewers ask.
Follow new case studies.
Requests and corrections welcome: open an issue on GitHub.
New case studies appear in the feed first. Any RSS reader works.