Mock system design interview at Pinterest

A live 45-minute round on a question reported in Pinterest interviews, run by an AI interviewer that asks one thing at a time, probes what you say, looks at your whiteboard, and weighs what that round is reported to weigh. It ends with a debrief: a score, what was strong, what was missing.

your question

Design a News Feed

The home timeline of Twitter, Instagram or Facebook: posts from people you follow, ranked, fresh, and fast for hundreds of millions of users.

You will not see the requirements, the numbers or the design before you start. That is the point.

Walk through it first

What the Pinterest round is reported to look like

45–60 minutes, product-shaped and usually close to what Pinterest runs: the home feed, recommendations, image storage and delivery, search or notifications.

What it weighs

Requirements, scale and latency settled before the first diagram
How Pins are chosen and ranked for each user, not only how they are stored
Images at scale: object storage, several sizes per image and delivery through a CDN
Tradeoffs named as you go, such as precomputing a feed against keeping it fresh

The common mistake

Treating ranking as a black box. Feed and recommendation designs are reported to be pushed toward how Pins are chosen and what happens for a new user with no history, not only toward storage and serving.

From public interview guides and candidate reports, and Pinterest’s own interview guidance where it publishes any. Not endorsed by Pinterest. The interviewer is an AI running in that style; it is practice, not a prediction.

Start the round

Timed · 45 minutesInterview conditions. The AI interviewer owns the clock; the AI Mentor is off.With the AI Mentor · untimedNo clock, and an AI Mentor beside you to ask when you are stuck.

The interviewer’s opening question is free. Answering it is part of Pro. See an example round and its debrief →

The 8 questions this round draws from

Each is reported in Pinterest interviews. Pick one to sit, or read its reference design and walk through a strong answer first.

Design a News FeedThe home timeline of Twitter, Instagram or Facebook: posts from people you follow, ranked, fresh, and fast for hundreds of millions of users.
drawn
Design a Web CrawlerFetch billions of pages a month politely, discover new links, skip duplicates, and keep the copy fresh without getting the crawler banned.
Design a Recommendation SystemThe “recommended for you” video home feed: 50 personalised videos picked from billions for 500 M daily users in under 200 ms.
Design Post SearchKeyword search over a billion users’ posts, searchable seconds after posting, sorted by recency or likes, hiding every post the searcher may not see.
Design a Social GraphLinkedIn’s connections for 1 B members: invitations, follows, a 1st/2nd/3rd badge on 200 k profile views a second, and daily People You May Know.
Design an Ad Serving SystemPick the best of 10 M active ads for 5 M requests a second in under 100 ms, within every campaign’s targeting, budget and frequency caps.
Design TikTokA full-screen feed of short videos for 1 B daily users, where the next clip starts instantly and every swipe reshapes what comes next.
Design PinterestSave images to boards, browse a personalised grid and search by picture: 100 M daily users, 5 B distinct images behind 100 B saves.

Other companies: Anthropic · Google · Meta · Amazon · OpenAI · Microsoft · Uber · DoorDash