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Design a News Feed: System Design Interview Practice

Design a News Feed as a system design interview question: Users follow others and see a feed of recent posts from the people they follow, newest or ranked…

How do you answer "Design a News Feed" in a system design interview?

Store posts once, then build each user's feed either at post time (fan-out on write: push the post id into every follower's cached feed) or at read time (fan-out on read: pull and merge followed accounts' posts). Large systems mix both: push for ordinary accounts, pull for celebrities, merge at read time, and page the result with cursors.

  • Level: Intermediate
  • Scored out of: 100
  • Cost: Free to read; a free account gets the review

Users follow others and see a feed of recent posts from the people they follow, newest or ranked first.

The scale

300 million daily users; the average user follows 200 accounts; some accounts have tens of millions of followers.

What a strong answer covers

  1. Requirements (20 points). States the functional requirements in scope and the non-functional ones that drive the design (scale, latency, availability, consistency), and leaves out what is out of scope.
  2. Scale estimates (15 points). Turns the stated scale into requests per second (average and peak), storage and bandwidth, with the arithmetic shown, and uses the numbers to make a decision.
  3. API and data model (20 points). Defines the main API calls with their inputs and outputs, and a data model whose keys and store fit the access patterns.
  4. Architecture (25 points). Chooses components that fit the requirements and explains how a request moves through them, for the main read and write paths.
  5. Bottlenecks and trade-offs (20 points). Names the real bottlenecks and failure points at this scale and how the design handles them, weighing the alternatives (consistency vs availability, push vs pull, cost).

How the practice works

Write your design in sections — functional and non-functional requirements, scale estimates, the API, the data model, the request flow and a deep dive on the bottlenecks — and pick the components to draw the architecture. A review scores it on the five areas above in under a minute, then you can defend it in an AI mock interview.

The reference design

Design a News Feed: the walkthrough, with animated figures.

Common questions

How do you answer "Design a News Feed" in a system design interview?

Store posts once, then build each user's feed either at post time (fan-out on write: push the post id into every follower's cached feed) or at read time (fan-out on read: pull and merge followed accounts' posts). Large systems mix both: push for ordinary accounts, pull for celebrities, merge at read time, and page the result with cursors.

What scale is "Design a News Feed" designed for here?

300 million daily users; the average user follows 200 accounts; some accounts have tens of millions of followers. Your estimates turn that into requests per second, storage and bandwidth before you pick components.

How is a design scored?

Out of 100 on a fixed rubric: requirements (20), scale estimates (15), api and data model (20), architecture (25), bottlenecks and trade-offs (20). The review names what the design covered and what it missed, then points to the reference design.

Is "Design a News Feed" a good first system design problem?

It is rated intermediate. Start with the beginner problems — the URL shortener and the rate limiter — and the System Design notes on load balancing, caching and sharding first.

Do I need an account?

Not to read the problem or the reference design. Getting your design reviewed needs a free account.

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