Design
WhatsApp Messenger
Design a real-time messaging system like WhatsApp supporting 1-1 chats, group messages, media sharing, and message status (sent/delivered/read).
01 - Why interviewers ask this
Messaging apps test delivery guarantees under real network unreliability — interviewers specifically probe how you achieve at-least-once delivery with correct read-receipt semantics.
02 - Where this system exists in the real world
You interact with this design every day.
WhatsApp / Telegram / Signal messaging platforms
Enterprise team chat tools (Slack, Teams)
Customer support live-chat systems
03 - What you'll master
Solve this once. Know it forever.
Guarantee message delivery under flaky connections
Model sent/delivered/read receipt states
Design group chat fan-out efficiently
04 - What you'll design
7 functional · 4 non-functional requirements.
Send and receive text messages in real-time
6 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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