System design interview question

Design Twitter / X (timeline, tweets)

Hard · System design (HLD) · Company tags: Twitter/X, Meta, Google, Microsoft, Uber

The prompt

"Design Twitter. Users post short text updates, follow other users, and open the app to a home timeline showing recent posts from everyone they follow. Assume 300M daily active users. Start wherever you like."

What this round really tests

Whether the candidate discovers that read and write amplification are in tension, and whether they reach a hybrid fan-out instead of picking one extreme. Everything else is scaffolding.

Clarifying questions worth asking

Timeline ordering: chronological or ranked?
Do we need media, retweets, replies?
Follower distribution?
Consistency requirements?
Do we need search / hashtags / DMs?
Delete and edit?

How the round usually runs

0–5 min: Scoping
5–8 min: Estimates
8–15 min: API + data model
15–25 min: Architecture
25–38 min: Deep dive
38–45 min: Wrap

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