Top 50 System Design Interview Questions (2026)
This is the definitive list of system design interview questions you should be able to answer in 2026. They are drawn from Glassdoor and Levels.fyi interview reports, Alex Xu's Volume 1 & 2, and direct mentor feedback from candidates who recently interviewed at Google, Meta, Amazon, Netflix, Stripe, Uber, Airbnb, and LinkedIn. Every question on this page has a corresponding interactive simulator on this site — click any title to open the walkthrough.
Difficulty ratings are calibrated against the bar at top-tier companies: EASY means you should solve it cleanly to pass, MEDIUM is the standard senior-level expectation, and HARD separates strong candidates from staff-level ones.
Tier 1 — Universal questions (asked everywhere)
If you walk into any FAANG system design round, expect one of these. Master all 10 first.
| # | Question | Difficulty | Asked at |
|---|---|---|---|
| 1 | URL Shortener | MEDIUM | All Bitly Google |
| 2 | WhatsApp / Chat System | HARD | Meta Apple Discord |
| 3 | News Feed / Timeline | HARD | Meta Twitter LinkedIn |
| 4 | YouTube / Video Streaming | HARD | Google Netflix TikTok |
| 5 | Google Drive / Dropbox | HARD | Google Dropbox Microsoft |
| 6 | Rate Limiter | MEDIUM | Uber Stripe Cloudflare |
| 7 | Distributed KV Store (Dynamo) | HARD | Amazon LinkedIn Apple |
| 8 | Search Autocomplete | MEDIUM | Google Amazon Yelp |
| 9 | Notification System | MEDIUM | Meta Airbnb Uber |
| 10 | Web Crawler | MEDIUM | Google Bing Apple |
Tier 2 — Senior / Staff level designs
These show up frequently for senior+ roles, especially at fintech and data-intensive companies.
| # | Question | Difficulty | Asked at |
|---|---|---|---|
| 11 | Payment System | HARD | Stripe PayPal Square |
| 12 | Stock Exchange / Trading Engine | HARD | Two Sigma Robinhood HRT |
| 13 | Kafka-style Message Queue | HARD | LinkedIn Uber Confluent |
| 14 | Metrics Monitoring (Prometheus) | HARD | Datadog Cloudflare Splunk |
| 15 | Nearby Friends / Snap Map | HARD | Snap Meta Strava |
| 16 | Google Maps / Routing | HARD | Google Lyft Uber |
| 17 | Ad Click Aggregation | HARD | Meta Google TikTok |
| 18 | S3-style Object Storage | HARD | Amazon Backblaze Google |
| 19 | Proximity Service (Yelp) | MEDIUM | Yelp DoorDash Uber |
| 20 | Hotel Reservation | MEDIUM | Booking Airbnb Expedia |
Tier 3 — Specialized data-intensive designs
Common at fintech, gaming, and real-time analytics companies.
| # | Question | Difficulty | Asked at |
|---|---|---|---|
| 21 | Digital Wallet (PayPal/Venmo) | HARD | PayPal Coinbase Robinhood |
| 22 | Distributed Email (Gmail) | HARD | Google Microsoft |
| 23 | Gaming Leaderboard | MEDIUM | Riot EA Roblox |
| 24 | Real-time Twitter Trending | HARD | Twitter/X Reddit |
| 25 | Distributed ID Generator (Snowflake) | MEDIUM | Twitter Discord Instagram |
Tier 4 — System internals (probe questions)
Senior interviewers probe these to separate "I read about it" from "I understand it."
| # | Question | Difficulty | Asked at |
|---|---|---|---|
| 26 | How does a B-Tree work? | HARD | All senior |
| 27 | Explain Raft consensus | HARD | All senior CockroachDB |
| 28 | B-Tree vs LSM-Tree trade-offs | HARD | All senior DBaaS |
| 29 | Database isolation levels | HARD | All senior |
| 30 | Two-phase commit | HARD | All senior |
| 31 | CRDTs for collaborative editing | HARD | Figma Notion Linear |
| 32 | Consistent hashing | MEDIUM | All |
| 33 | Quorum reads/writes | MEDIUM | All senior |
| 34 | CAP theorem in practice | MEDIUM | All |
| 35 | DNS resolution flow | MEDIUM | All |
Tier 5 — DSA in system design context
Building blocks that anchor the larger systems above.
| # | Question | Difficulty | Asked at |
|---|---|---|---|
| 36 | LRU Cache implementation | MEDIUM | All |
| 37 | Bloom Filter design | MEDIUM | Google Akamai Cassandra |
| 38 | Consistent hashing with vnodes | MEDIUM | All |
| 39 | Trie for autocomplete | MEDIUM | Google Amazon |
| 40 | Segment Tree for range queries | HARD | Google Quant |
| 41 | Dijkstra for routing | MEDIUM | Google Lyft |
| 42 | Union-Find for connectivity | MEDIUM | Meta All |
| 43 | Count-Min Sketch for trending | HARD | Twitter Cloudflare |
| 44 | Token Bucket rate limiting | MEDIUM | All |
| 45 | Merkle Tree for anti-entropy | HARD | Cassandra Bitcoin |
Tier 6 — Estimation & meta-questions
Open-ended questions that test whether you can think out loud about scale and operations.
| # | Question | Difficulty | Asked at |
|---|---|---|---|
| 46 | Estimate QPS for Instagram | MEDIUM | All |
| 47 | Scale a single server to 10M users | MEDIUM | All |
| 48 | Build a back-of-envelope estimator | EASY | All |
| 49 | What happens when you type a URL in browser? | MEDIUM | All |
| 50 | Debug high p99 latency in production | HARD | All senior |
How does this site help you practice these questions?
Most "top X system design questions" lists are static text. Here, every question on the list links to an interactive simulator that you can actually use:
| Resource | Has the list? | Interactive practice? | Capacity estimates? | Free? |
|---|---|---|---|---|
| System Design Simulator (this site) | All 50 with full walkthroughs | 106 simulators, browser-based | Per-design capacity math | 100% free |
| GitHub system-design-primer | Concept lists | No | Some | Free |
| Educative System Design course | ~25 designs | No | Yes | Paid |
| Alex Xu books | ~26 designs | No | Yes | Paid |
| Random YouTube playlists | Partial | No | Sometimes | Free |
Frequently asked questions
Are these the same questions asked at FAANG companies in 2026?
Yes. The list is calibrated against recent (2024–2025) interview reports from Glassdoor and Levels.fyi, supplemented with mentor feedback from candidates who recently went through loops at Google, Meta, Amazon, Netflix, Apple, and Stripe. Tier 1 questions are universal — they appear at virtually every company.
How long should I spend on each question?
Plan 2–3 hours for a medium question (read walkthrough, run simulator, take notes, work the trade-offs) and 3–5 hours for a hard question. The full Tier 1 (10 questions) takes about a week of focused study.
Should I memorize all 50?
No — you should understand the patterns underlying them. URL Shortener teaches base62 + caching + sharded read path. WhatsApp teaches connection management + fan-out + ordering. Once you internalize the patterns, novel questions become applications of patterns you already know.
What's the order to study these?
Follow our 8-week roadmap — it sequences these questions by dependency. Otherwise: Tier 1 first (10 questions), then any 5 from Tier 2 that match your target companies, then Tier 4 internals as deep-dive prep.
Ready to practice? Open the simulator
All 106 simulators are free, browser-based, and require no sign-up.
Open System Design Simulator →→ Open the 8-Week Study Roadmap · All 27 HLD Walkthroughs · 32 System Internals