Design a notification center
mediumComplete guide with examples and interview questions · 40 min
Say it out loud in an interview — clear, simple, no textbook wording.
If someone asks me to design a notification center, I would say it is a feed where every item has a read state, a destination, and a reason to exist. The bell, the list, and the unread count are one system. When they disagree, users stop trusting all three.
Interviewers care because notifications look trivial and fail in specific ways. Counts that drift, like storms that bury mentions, and read states that reset on refresh are all frontend state bugs, not backend mysteries. The question tests whether you treat the count as a correctness requirement.
The senior nuance is grouping with restraint. Grouping is what keeps a busy user sane, and over-grouping is what hides the one mention they needed. The rule for what groups and what never groups is the design.
Key takeaways
- •A notification center is a feed with read state, grouping, and routing
- •Grouping by actor and action prevents a like storm from burying real updates
- •Unread counts must be exact and consistent everywhere, or users stop trusting them
- •Marking read is a user action with a server round trip, not a local paint
- •Preferences (what notifies, where) are part of the design, not a settings afterthought
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