System designEasysd-g559

Subject NotificationsLevel Entry–Mid~25 minCommon in Distributed systems interviewsIndustries Software development, Technology

Question

Design an in-app notification system for a small product (the bell icon with a list of 'someone commented on your post', 'you were mentioned', etc., and an unread count). A few thousand users. When an event happens, the relevant users should see a new notification and an updated unread badge. Describe the data model and how the unread count stays fast.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

Loading whiteboard…

Run or narrate your approach, then ask the coach.