Mock system design interview at Snap

A live 45-minute round on a question reported in Snap 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 Snap round is reported to look like

60 minutes, product-shaped and tied to Snap features: messaging, photo and video sharing, notifications, feeds or friends on a live map.

What it weighs

Ephemeral data: expiry and deletion built into storage, not added afterwards
Low latency for a mobile-first app, including real-time delivery
Large photos and videos: storage, processing and delivery through a CDN
A design tied back to the feature and what the user sees

The common mistake

Keeping everything forever by default. Much of what Snap handles is meant to expire, and candidates are advised that this changes the architecture, so design expiry and deletion in from the start.

From public interview guides and candidate reports, and Snap’s own interview guidance where it publishes any. Not endorsed by Snap. 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 9 questions this round draws from

Each is reported in Snap 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 InstagramUpload photos, publish posts and stories, and load a feed of them for 500 M daily users, with every image served from a CDN in milliseconds.
Design TinderShow each person a deck of nearby profiles that fit both people’s preferences, never repeat one, take 2 billion swipes a day, and announce a match the instant two people like each other.
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 Nearby FriendsShow each user which friends are within 5 miles, refreshed every 30 s, for 10 M concurrent users, without leaking anyone’s location.
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.
Design a Content Moderation SystemCatch spam, nudity, hate and illegal media in 4 billion daily posts and comments before they spread, with 15,000 reviewers for the hard cases.

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