What to work through
Work through a notification system as a spoken system design interview. Start by clarifying the scope, sketch a working design and explain the trade-offs behind your choices.
- Open a list of past notifications that loads more as the person scrolls
- Show new notifications as they arrive, in the list and in a count of unread ones
- Mark one notification or all of them as read, on every device the person uses
- Let any part of the app show a short pop-up message that closes by itself
Constraints to discuss
- The unread count agrees across open tabs and devices within seconds
- No notification shows twice or goes missing after a reconnect
- A pop-up never takes focus and is still announced to a screen reader
- A tap on a notification answers within 200 milliseconds
- A tab left in the background does almost no work
Need a starting point?
Watch for these common gaps as you prepare:
- Page numbers for a list that new items keep shifting
- Adding up the unread count on the client instead of taking the server's
- Moving focus to each pop-up, or giving it no announcement at all
- Pop-ups that close before a person can reach their action, with no other way to do it
- Reconnecting after time away without fetching what was missed
Why this question is in the collection
These sources connect the problem to company interview reports or preparation guides. They do not guarantee what a company will ask you.
- Roblox: A Staff or Principal frontend candidate tip from June 2026: design a notification system. The interviewer asked how the server makes unique ids and how the pagination cursor works, and went deep on live updates and the API.
- Roblox: A frontend candidate tip from May 2026: a global notification system, which leaned toward full-stack design.
- Roblox: A Blind thread on the IC4 front end design round, dated September 3 with no year shown: a commenter names a notification system as one of two recent questions.
- Roblox: Listed by PracHub in September 2026 as a frontend engineer question, with no candidate narrative: a notification list with its history and live updates.
- Amazon: An AWS front end engineer at L6 reports an onsite design round about August 2026: notification pop-ups at three levels, at most five at a time with the newest first, each closing on a timer and callable from any component. The follow-up asked what happens when more than five arrive.