Mock system design interview at LinkedIn

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

45–60 minutes, usually product-shaped around surfaces LinkedIn runs: the feed, messaging, notifications, search and typeahead, connection recommendations.

What it weighs

Product sense: what the member sees, judged alongside the architecture
The graph underneath: fan-out, and the skew between typical members and accounts with very large followings
Scale numbers for a member base of around a billion
Availability, security and how the system is run, not only how it is built

The common mistake

Making good choices silently. Interviewers are reported to score the reasoning they hear, so name the options, pick one, say why, and tie it back to what the member experiences.

From public interview guides and candidate reports, and LinkedIn’s own interview guidance where it publishes any. Not endorsed by LinkedIn. 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 14 questions this round draws from

Each is reported in LinkedIn 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 Notification SystemDeliver push, email, SMS and in-app notifications to hundreds of millions of users: the right channel, once, on time, and never at 3 a.m.
Design a Rate LimiterA distributed service that decides, in under a millisecond, whether a request from a client is allowed under its quota.
Design Search AutocompleteSuggest the top ten completions after every keystroke, in under fifty milliseconds, from what the world searched for in the last hour, without suggesting anything that gets you in the newspaper.
Design an Ad Click AggregatorCount a million ad clicks a second, show advertisers a dashboard that is seconds behind, stop a campaign the moment its budget runs out, and be exactly right when the invoice is cut.
Design a Project-to-Contractor Matching SystemMatch posted projects with qualified, available contractors across a 500 k-person talent pool, and learn from who actually gets hired.
Design a Distributed Message QueueA Kafka-style log that ingests a million messages a second, keeps them in order per key, replicates them so no acknowledged message is lost, and lets many consumer groups read at their own pace.
Design Live CommentsComments and reactions on live video that reach viewers within two seconds, at 50 M concurrent viewers and 5 M on one stream.
Design a Top-K Heavy Hitters ServiceRank the top 1,000 videos by views over the last minute, hour, day and all time, from a million views a second.
Design Google SearchSearch 50 billion pages at 100 k queries a second: the ten best results with snippets in under 200 ms, and news within minutes.
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 Google NewsCollect 2 M articles a day from 50,000 publishers, group them into stories, rank them per edition, and serve 300 M daily readers.
Design an A/B Testing PlatformRun 500 experiments at once on 300 M users: sticky variants in microseconds, exposure logging, and confidence intervals teams can trust.

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