Practice: Chat App (WhatsApp / Messenger)

One-to-one and group messaging with delivery receipts, offline support and message ordering.

45-minute interview simulation

You will move through 7 stages, each with a time budget. Type your answer as you would say it out loud. The reference answer is hidden until the review. Going over time is allowed, but it is tracked.

Requirements — 5 min
Back-of-envelope estimates — 5 min
API design — 5 min
Data model — 5 min
High-level design — 10 min
Deep dives — 10 min
Trade-offs & wrap-up — 5 min