System Design AI

Guided practice

Start with a template. Work through each step. Ask Coach when you need a second opinion.

Classic designs 115

Ordered by design number

Company tags are community-reported. Counts on cards show how many people reported that design.

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1. Design a URL Shortener
Create short links, resolve them quickly and handle expiry without sending users to the wrong destination.
ClassicEasy
Caching Databases API design
+8
AWS Base62 CloudFront DynamoDB ID generation Key value store Redirects URL shortening
Worked design
Practice
2. Design a Distributed Rate Limiter
Enforce tenant quotas across servers while making burst behavior and outage policy explicit.
ClassicMedium
Caching Databases Concurrency
+8
Distributed systems API gateways AWS Lua Rate limiting Redis Reliability Token bucket
Worked design
Practice
3. Design a Distributed Cache
Partition cached data, survive node loss and keep cache misses from overwhelming the source of truth.
ClassicMedium
Caching Sharding Databases
+9
Distributed systems AWS Consistency Consistent hashing Hot keys LRU eviction Memcached Redis Replication
Worked design
Practice
4. Design a Notification System
Deliver email, push and SMS with preferences, retries and honest delivery status.
ClassicMedium
Queues Streaming Distributed systems
+10
AWS Delivery semantics Fan out Kafka Notifications Real time Reliability Retries Amazon SQS User preferences
Worked design
Practice
5. Design a Chat System
Send durable messages, reconnect devices and explain ordering and delivery receipts.
ClassicMedium
Databases Security Privacy
+11
Distributed systems AWS Chat DynamoDB End to end encryption Messaging Multi region Offline first Ordering Redis Pub/Sub WebSockets
Worked design
Practice
6. Design a News Feed
Build a paginated feed that handles high-fan-out authors, fresh posts and visibility changes.
ClassicMedium
Caching Databases Streaming
+11
Privacy Distributed systems AWS DynamoDB Fan out Kafka News feed Pagination Redis Social Timeline
Worked design
Practice
7. Design a File Storage Service
Upload and share large files with resumable transfer, versions and safe metadata changes.
ClassicMedium
Databases Object storage Security
+9
AWS Deduplication DynamoDB File sync Large files Multipart upload Permissions Versioning WebSockets
Worked design
Practice
8. Design a Video Streaming Platform
Turn uploads into playable renditions and serve viewers through unreliable networks.
ClassicHard
Queues Object storage Adaptive bitrate
+6
AWS Capacity planning CDNs Multipart upload Transcoding Video streaming
Worked design
Practice
10. Design an API Gateway
Route API traffic with authentication, tenant limits and safe configuration rollout.
ClassicMedium
Security API design API gateways
+7
Authentication AWS Control plane Envoy Rate limiting Reliability Routing
Worked design
Practice
11. Design a Container Orchestrator
Reconcile desired workloads, schedule containers and recover from failed nodes safely.
ClassicHard
Distributed systems AWS Control plane
+6
etcd Isolation Kubernetes Orchestration Reconciliation Scheduling
Worked design
Practice
40. Design an Ad Click Aggregator
Count every ad click once, fast enough to chart live and exactly enough to bill. One-hour interview boards for junior, senior and staff: requirements, data layer, low-level design and what goes wrong at every component.
ClassicMedium
Databases Streaming Distributed systems
+6
AWS DynamoDB Exactly once Flink Kafka Reconciliation
Worked design
Practice
42. Design a Metrics Monitoring Platform
Collect 5 million samples a second from 500,000 hosts, store them as time series, chart them and page people.
ClassicMedium
Databases Streaming Observability
+7
Distributed systems Alerting AWS Cardinality Kafka Prometheus Time series
Worked design
Practice
43. Design YouTube Top-K
The K most-viewed videos for the last hour, day, month and all time from 700,000 views a second, exactly and in milliseconds.
ClassicMedium
Caching Databases Streaming
+7
Distributed systems AWS Flink Kafka Redis Sliding windows Top-K
Worked design
Practice
44. Design a Price Tracking Service
Watch prices on 500 million products with a polite crawler and a million browsers, verify what you are told, and notify subscribers within minutes of a drop.
ClassicMedium
Databases Streaming Distributed systems
+6
AWS Crawling Crowdsourcing DynamoDB Kafka Notifications
Worked design
Practice
45. Design a Job Scheduler
Run 10,000 jobs a second within two seconds of their time, at least once, with retries, fairness between tenants and exactly-once effects.
ClassicMedium
Queues Databases AWS
+5
Cron DynamoDB Idempotency Scheduling Amazon SQS
Worked design
Practice
46. Design a Web Crawler
Ten billion pages in five days, politely, without losing progress: fetchers and parsers, domain locks, bandwidth math, deduplication and a crawl that stays fresh. One-hour boards for junior, senior and staff.
ClassicMedium
Queues Object storage AWS
+5
Crawling Deduplication Politeness Amazon S3 Amazon SQS
Worked design
Practice
47. Design an Online Judge like LeetCode
Run strangers' code safely in single-use microVMs, return verdicts within 5 seconds, and rank 100,000 contestants live.
ClassicMedium
Caching Queues Databases
+8
Security AWS Firecracker Leaderboards Online judge Redis Sandboxing Amazon SQS
Worked design
Practice
48. Design a Ticket Booking System like Ticketmaster
Hold seats with one conditional write, pay by authorize and capture, and put ten million fans in a fair waiting room without selling a seat twice.
ClassicMedium
Search Concurrency Aurora
+5
AWS Booking OpenSearch Ticketing Waiting room
Worked design
Practice
49. Design an Online Auction like eBay
Take bids on 10 million live auctions with one consistent highest bid, lose none, push the price to every watcher and end each auction fairly.
ClassicMedium
Streaming Concurrency Distributed systems
+7
Auctions Aurora AWS Contention Kafka Real time Server sent events
Worked design
Practice
50. Design a Ride-Sharing Service like Uber
Price a trip, match a rider to a nearby driver who has ten seconds to accept, and never give one driver two rides.
ClassicMedium
Caching Databases AWS
+6
Geospatial Matching Redis Ride sharing Step functions WebSockets
Worked design
Practice
51. Design a Local Delivery Service like Gopuff
Show what 10,000 small warehouses can deliver within the hour in under 100 ms, and take multi-item orders without ever selling a unit twice.
ClassicMedium
Caching Transactions Aurora
+4
AWS Change data capture Geospatial Inventory
Worked design
Practice
52. Design a Payment System like Stripe
Charge cards through the networks exactly once: idempotency keys, a card vault, timeouts as unknowns, signed webhooks, a double-entry ledger and reconciliation. One-hour boards for junior, senior and staff, with the theory behind them.
ClassicMedium
Streaming Distributed systems AWS
+6
Idempotency Kafka Ledger Payments PCI compliance Reconciliation
Worked design
Practice
53. Design a Stock Trading App like Robinhood
Live prices to five million phones through per-symbol pub/sub, and market and limit orders over FIX that are never lost, sent twice or overspent.
ClassicMedium
Queues AWS FIX protocol
+5
Publish / subscribe Real time Reconciliation Trading WebSockets
Worked design
Practice
54. Design a Photo Sharing App like Instagram
Photos and videos for 500 million daily users: presigned multipart uploads, a processing pipeline, CloudFront and a hybrid fan-out feed.
ClassicMedium
Caching Databases Object storage
+7
AWS CDNs Fan out Instagram Media upload Redis Amazon S3
Worked design
Practice
55. Design a News Aggregator like Google News
Collect from 20,000 publishers by push, polls and crawls, file each article once into feeds by region and category, and serve a billion pages a day from the edge.
ClassicMedium
Caching AWS CloudFront
+4
Feeds News aggregator Pagination RSS
Worked design
Practice
56. Design a Local Business Review Site like Yelp
Search 10 million businesses by place, words and category, keep every average rating exact, and keep fake reviews out.
ClassicMedium
Databases Search AWS
+5
Change data capture Geospatial OpenSearch PostgreSQL Reviews
Worked design
Practice
57. Design Post Search like Facebook
Search a billion posts a day by keyword, newest or most liked first, with an inverted index you build yourself.
ClassicMedium
Caching Databases Streaming
+7
Search Distributed systems AWS DynamoDB Inverted index Kafka Redis
Worked design
Practice
58. Design a Dating App like Tinder
Stacks of nearby people in under 300 ms, 2 billion swipes a day, and a match never missed even when both like at once.
ClassicMedium
Caching Databases Search
+7
AWS Bloom filter Consistency DynamoDB Geospatial OpenSearch Redis
Worked design
Practice
59. Design a Fitness Tracking App like Strava
Record runs and rides on the phone without signal, upload each once, show them to friends and rank athletes by week, month and year.
ClassicMedium
Caching Databases AWS
+6
DynamoDB Fitness GPS Leaderboards Offline first Redis
Worked design
Practice
60. Design Live Comments like Facebook Live
Live comments for millions of viewers: SSE streams, a Redis channel per video with co-located viewers, sampling and CDN snapshots for hot videos.
ClassicMedium
Databases AWS DynamoDB
+5
Fan out Live comments Real time Redis Pub/Sub Server sent events
Worked design
Practice

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