# Design Twitter: system design interview question

> Celebrity traffic, follow changes, and post deletion make a complete home timeline hard to serve within a fixed latency target.

Source: https://sysround.com/questions/design-twitter
Updated: 2026-11-05


Difficulty: hard. Levels: Mid-level, Senior, Staff+.

## How the interviewer opens it

"Design a microblogging platform like Twitter. People can publish short posts, follow accounts, reply to posts, and repost posts. Some accounts have millions of followers."

## What to clarify first

- Audience and peak traffic
- Read and write mix
- Follow counts and celebrity accounts
- Home contents
- Latency
- Consistency and availability
- Durability and retention
- Follow changes and deletion
- Content and home history
- Deployment and exclusions

## Scope of a strong answer

Core requirements:

- Create and delete short posts, replies, and reposts.
- Follow and unfollow public accounts.
- Read the latest 1,000 eligible home entries, with the newest first.
- Read account timelines and reply threads.

Usually out of scope:

- Media uploads and video delivery.
- Search, trends, and ranked recommendations.
- Private accounts and private messages.
- Ads and notifications.
- Global write availability.

## What interviewers probe

### Traffic from popular accounts

One publication can reach 50 million followers. The service must prevent this work from delaying other authors or overwhelming home reads.

### Timeline order and page boundaries

Many sources contribute entries at different times. The service must preserve page order without reading every followed account's full history.

### Follow changes and post removal

Visibility changes can remove most recent candidates. Older eligible posts must remain available without a large scan or edits to every cached reference.

## Common mistakes

- The design treats every author the same despite the difference between typical accounts and celebrities.
- The publication request waits for every follower's home update.
- The read plan ignores the maximum follow count and users who return after a long absence.
- The design caps candidates at 1,000 before visibility checks and provides no source for older eligible entries.
- The pagination plan ignores late delivery and distinct repost identities.
- The design treats cached references as the authority for follows and deletion.

## The bar by level

- **Mid-level:** Defines posts, follows, replies, and reposts. Builds a working home flow with cursor pagination. Explains celebrity traffic and provides a source refill path.
- **Senior:** Quantifies fanout and bounded source reads. Handles returning users, visibility changes, retries, and page limits. Meets latency and freshness targets during normal operation.
- **Staff+:** Defines cache coverage and safe delivery changes. Bounds worst-case refill work and shard requests. Plans replay and recovery while stating failure behavior and capacity limits.

Practice this question with an AI interviewer: https://sysround.com/practice/new?problem=twitter


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SysRound (https://sysround.com) is an AI practice tool for system design interviews. It has a voice or typed AI interviewer and a shared whiteboard. At the end, you get feedback on each skill and a model answer. The AI feedback can be wrong.