Design a Typing Indicator · System Design Interview

Design a Typing IndicatorDesign the "is typing…" signal in a chat product: when someone types, the others in the conversation see it quickly, and it disappears when they stop.What it has to do

Show other participants that someone is typing

Stop showing it shortly after they stop or send

Work for one-to-one chats and for groups

Scale

Concurrent chat users: 20 million

Largest group: 1,000 members

Out of scope

Message delivery and storage

Read receipts

Presence and online status

Push notifications

Practise this challengeAll system design challenges

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