Design Twitter
PremiumProduct architectureMedium
- Home timeline
- Hybrid fan out
- Celebrity problem
Quick answer
This product architecture interview question asks you to design Twitter. Aim for a design that meets its requirements at the stated scale, then explain its main components, data flow and trade-offs. Interviewers want to see how you scope the problem, size it and defend each choice.
The problem
Design Twitter (now X), a microblogging app where users post short tweets, follow other accounts and read a home timeline of tweets from the people they follow. The hard parts are building timelines for 250 million daily users when one account has 100 million followers, and counting likes on a viral tweet without one hot row.
What must the system do?
- Post a tweet: Up to 280 characters and 4 media IDs; it reaches followers' home timelines within 5 seconds for normal accounts.
- Home timeline: Tweets and retweets from followed accounts, newest first, 50 per page, paging back up to 800 tweets.
How well must it do it?
- Fast timeline: A home timeline page of 50 tweets returns in under 300 ms at p99.
- Fresh enough: Tweets reach followers within 5 seconds for most accounts and within 1 minute for the largest; counts may lag up to 10 seconds.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Home timeline
- Hybrid fan out
- Celebrity problem
- Timeline cache
- Sharded counters
- Follow graph
How you’ll practise
- Requirements
- Core entities
- API design
- Client and server flow
- Scale and edge cases
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any product architecture design round.
- Clarifies the requirements before drawing anything
- Uses a few numbers that actually change the design
- Draws a clear path from the client to storage
- Picks storage and caching with reasons, not by habit
- Explains what breaks first under load and how to fix it
- States trade-offs openly instead of claiming a perfect design
Questions people ask about this interview question
- Which design type is this question?
- It is a product architecture question. You design Twitter and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Medium. Entry-level engineers can practise it, but it expects you to reason about requirements and trade-offs, not only list components.
- What should I cover first?
- Start with the requirements: what the system must do, how well it must do it and which numbers change the design. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team