AnthropicVerified interview challenge
Design a 1-on-1 chat system
Design fast message delivery for online users and reliable recovery for people who reconnect later.
Unlock with Full AccessThe challenge
Build a large chat service with long-lived connections, presence information and durable message history. Explain how a message travels from sender to recipient, what an acknowledgement means and how the system handles retries or disconnections. Your design also needs a defensible choice of message bus.
- A focused messaging problem
- The scenario covers one-to-one conversations with one web device per user. Group chats and channels are outside the task.
What you'll practise
Delivery guarantees
Explain ordering, acknowledgements and duplicate handling through the message lifecycle.
Connections and recovery
Track presence and recover missed messages after a recipient disconnects.
Scaling the service
Defend storage, partitioning and message-bus choices against the traffic and availability targets.
Your canvas
SenderMessages & retries
RecipientLive & offline delivery
The interview, drawing canvas and final report are included with Full Access.