How the interviewer opens it
“Design an e-book platform that lets users download books and read across devices. Users can change reading positions, notes, and highlights while offline.”
The prompt is vague on purpose. The first minutes are for you. Reduce the prompt to the core features and agree on the numbers before you draw.
What to clarify first
- Scale
- Read and write mix
- Latency
- Offline use and durability
- Consistency and availability
- Reading positions
- Conflicting notes and highlights
- Book format and editions
- Access and exclusions
- Retention
The interviewer has the answers. In a SysRound round, Alex gives these answers, as a real interviewer does.
Scope of a strong answer
Core requirements
- Download books for offline use after an access check
- Sync reading positions across devices
- Create, edit, and delete notes and highlights while offline
- Reconcile changes without silently losing note text
Usually out of scope
- Book purchases and payments
- Publisher uploads and file conversion
- DRM and immediate access revocation
- Shared notes and live group edits
- Book recommendations
What interviewers ask about
- Changes after offline use
- Offline devices can edit or delete the same note. Retries and expired history must not lose text or restore deleted objects.
- Reading positions across devices
- An earlier position can reflect user intent. Arrival order and client clocks cannot reliably identify the desired resume position.
- Notes inside a book
- Page layouts vary across devices. Book revisions can move or remove the passage that a highlight identifies.
- Book downloads and access
- Downloads must survive interruption and remain usable offline. Access checks must not make every page depend on a server.
Common mistakes
- The design always uses the greatest page number as the resume position.
- The server trusts client clocks to order edits across devices.
- The server replaces conflicting note text without preserving a recovery copy.
- The server removes deletion records before old devices return.
- The client uses displayed page numbers as permanent highlight anchors.
- The sync service handles every book byte and every local page access.
The bar by level
- Senior (L5/E5)
- Defines durable local edits, atomic server changes, and duplicate protection. Resolves note conflicts and deletions without silent loss. Handles divergent positions and expired sync cursors.
- Staff (L6+/E6+)
- Proves that snapshots, history expiry, and delayed operations preserve correctness. Defines account ownership during regional failure. Quantifies delivery and history costs. Separates product conflict rules from technical order.
Sources · 1 reference
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SysRound · 1 record
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Design an e-book platform like Kindle
Reported date not specified
Source snapshot: Nov 12, 2026
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