Design WhatsApp
A complete 45-minute mock covering WebSocket gateways, message ordering, and offline delivery.
First win
You can defend per-conversation ordering and multi-device fanout.
Best for
Engineers prepping for FAANG system design interviews
Needs
Mac, Microphone, Whiteboard tool (Excalidraw, Figma, etc.)
Example outcome
A chat system becomes a full 45-minute mock.
This preview shows the interview shape: requirements, API, and the WebSocket gateway / message ordering / offline delivery deep dives.
Mock interview
Phases hit
6
Requirements, core entities, API, high-level design, deep dives, and wrap-up walked end-to-end with concrete numbers.
Deep dives
Two or three subsystems
You drive the most interesting tradeoffs unprompted with sub-100ms numbers when needed.
Wrap-up
You name what you optimized for and what you gave up out loud.