System design interview questions, grouped by what they test.
These are the system design interview questions in the Interview Hero library. Each one lists what a strong answer covers, not a model solution — the point is to practise saying it yourself, with someone asking why.
10 system design interview questions, in 4 themes.
Each question shows what it asks and what a strong answer should cover. Model answers are left out on purpose: you practise saying it yourself.
Read-heavy services and caching
2 questionsMost traffic is reads. The interview is about where the hot path is served from and what you precompute.
Design a URL shortener
Design a service that turns long URLs into short links and redirects visitors.
Scope: Cover id generation, read-heavy traffic, caching, and analytics.
Warm-upurl shortenerhashingcachingPractise this with RemyDesign search autocomplete
Design typeahead suggestions for a search box that serves millions of users.
Scope: Cover the data structure, how suggestions are ranked, freshness, and the read path.
StandardsearchtriecachingPractise this with Remy
Feeds, messaging and fan-out
4 questionsOne write reaches many readers. Expect questions about push versus pull, ordering, and the account with ten million followers.
Design a social news feed
Design a home feed that shows posts from the people a user follows.
Scope: Cover fan-out, ranking, freshness, and how you handle very popular accounts.
Hardnews feedfan outrankingPractise this with RemyDesign a real-time chat system
Design one-to-one and group chat with delivery receipts and history.
Scope: Cover connection management, ordering, offline delivery, and message storage.
HardchatwebsocketsorderingPractise this with RemyDesign a notification service
Design a service that sends push, email, and SMS notifications to a large user base.
Scope: Cover the pipeline from event to delivery, retries, deduplication, and user preferences.
Standardnotificationsqueuesfan outPractise this with RemyDesign a live video streaming platform
Design live streaming where creators broadcast to many viewers.
Scope: Cover ingest, transcoding, delivery, latency targets, and what happens when a stream goes viral.
HardvideostreamingcdnPractise this with Remy
Coordination across machines
2 questionsMany servers have to agree on a count or on who runs a job. The follow-ups go to failure and retries.
Design a distributed rate limiter
Design a rate limiter for a public API used by many clients.
Scope: Cover the algorithm, where the state lives, limits per client, and what happens when the limiter itself fails.
Standardrate limitingdistributed systemsreliabilityPractise this with RemyDesign a distributed task scheduler
Design a system that runs scheduled and recurring jobs across a fleet of workers.
Scope: Cover scheduling, retries, exactly-once effects, and what happens when a worker dies mid-job.
Standardtask schedulingqueuesidempotencyPractise this with Remy
Data at scale: storage and IDs
2 questionsWhere bytes and identifiers come from, and what stays consistent when machines, clocks or regions disagree.
Design a unique id generator
Design a service that issues globally unique ids at high volume.
Scope: Cover coordination, clock behavior, ordering, and how ids stay sortable.
Standardunique idssnowflakeclock skewPractise this with RemyDesign a file storage and sync service
Design a cloud drive that stores user files and syncs them across devices.
Scope: Cover chunking, deduplication, consistency, conflict handling, and multi-region durability.
Hardfile storagededuplicationconsistencyPractise this with Remy
What every one of these questions tests
Requirements first
Read-heavy or write-heavy, how fresh, how many users. The design follows from the numbers you ask for.
The hot path
Which request happens most, where it is served from, and what you precompute to keep it fast.
What fails
Every question here has a follow-up about a node, a store or a region going away.
Practise any of them on a whiteboard, out loud.
Pick a question
Start a system design round and choose any question below, or let the plan pick one for your interview.
Sketch and talk
Draw on the whiteboard while you explain. Remy follows the diagram and asks about the parts that matter.
Redo the weak moment
The report points at the moment the design wobbled. Redo just that part until it holds.
About these questions
Are there model answers for these system design questions?
Not here. Each question lists what a strong answer covers. You practise the answer out loud with Remy, and the report shows what to tighten.
Which system design question should I start with?
The warm-up questions, such as the URL shortener. They cover caching and ID generation, which the harder questions build on.
Do new questions get added?
Yes. This page is generated from the same library the app uses, so it lists every system design question you can practise.
More ways to practise
Pick a question and practise it with Remy.
Your first two practices are free. No card needed.
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