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Mobile System Design prompt pack
Mobile system design prompts with the constraints interviewers actually care about: offline state, sync, cache correctness, battery, memory and lifecycle recovery.
Use this in practice
Use these prompts to rehearse mobile-specific system design. For each prompt, start from the device and user state before you draw services.
Prompt 1: personalized feed
- Design a feed that opens fast, supports pagination, survives poor network and lets the user keep reading previously loaded content offline.
- Cover: initial load, pull to refresh, cursor pagination, cache storage, stale content labels, optimistic actions, image prefetching and memory pressure.
- Failure modes: duplicate items after refresh, missing items after pagination, stale likes, old responses overwriting new state, cache growing without bounds.
- Senior tradeoff: explain when you choose cached-first, network-first or stale-while-revalidate, and how the UI tells the truth without feeling broken.
- Metrics: feed open time, first contentful item, scroll hitch rate, image cache hit rate, pagination failure rate and stale response drops.
Prompt 2: offline notes
- Design notes that can be created, edited and deleted offline, then synced across devices later.
- Cover: local IDs, operation log, conflict policy, tombstones, retry queue, last-write-wins risks, user-visible conflict resolution and account switching.
- Failure modes: deletion resurrects a note, edits apply out of order, the same note appears twice, sync drains battery, app is killed mid-sync.
- Senior tradeoff: decide where conflict resolution belongs, client, server or user flow, and explain why that choice is acceptable for the product.
- Metrics: sync success rate, unresolved conflicts, retry age, local queue depth, data loss reports and battery impact during background sync.
Prompt 3: image loading layer
- Design an image pipeline for a high-scroll app with avatars, thumbnails and detail images.
- Cover: memory cache, disk cache, request coalescing, cancellation, priority, decoding off the main thread, placeholders and progressive loading.
- Failure modes: wrong image in reused cells, scroll jank from decoding, runaway memory, cache poisoning, duplicated downloads and no cancellation during fast scroll.
- Senior tradeoff: explain separate policies for avatars, feed thumbnails and full-screen images instead of using one cache rule for everything.
- Metrics: cache hit rate by tier, decode time, main-thread work, memory warnings, cancelled requests and visible image swap errors.
Prompt 4: background upload
- Design reliable photo or video upload from mobile when the app can be backgrounded, killed or moved between Wi-Fi and cellular.
- Cover: resumable upload, local pending state, background sessions, retry policy, user cancellation, compression, progress persistence and server idempotency.
- Failure modes: duplicate uploads, lost progress after kill, retry storm, upload completes but UI says failed, user logs out mid-upload.
- Senior tradeoff: define what happens if the upload is important enough to preserve but not important enough to drain battery.
- Metrics: completion rate, retry count, median upload time, stuck uploads, duplicate server objects and background termination events.
Answer shape
- Open with constraints: device lifecycle, network variability, local storage, memory, battery, privacy, release risk and team ownership.
- Define state ownership before components: what lives in memory, on disk, on the server, in the queue and in UI state.
- Draw the happy path only after naming offline, retry, stale response and app-kill behavior.
- Add observability: logs, counters, sampled traces, debug screens and support tooling for reproducing user state.
- End with evolution: migrations, feature flags, compatibility with older app versions and how teams own the boundaries.
Go deeper
Mobile System Design blueprint
Practice the decisions behind evolving, migrating, releasing and operating real mobile systems.
Altitude - the missing bridge between senior mobile Engineer and staff Engineer
Think like a staff-level mobile systems engineer across client, backend, security, reliability and production tradeoffs.
Use this resource inside a path.
The free tools are designed to plug into the larger Salari career system.
