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Classic designs 23

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
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
39. Design a Calendar System
Google Calendar-style events with recurrence, RSVPs and on-time reminders, using CDC for change notifications and a delay queue for reminders.
ClassicMedium
Caching Queues Databases
+5
Calendar Change data capture Notifications PostgreSQL Scheduling
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
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
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
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
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
61. Design a Collaborative Editor like Google Docs
A hundred people typing in one document, every copy converging, nothing acknowledged lost: one owner per document, an op log with snapshots, and fenced failover.
ClassicMedium
Databases Distributed systems AWS
+6
Collaboration Consistent hashing DynamoDB Operational transform Real time WebSockets
Worked design
Practice
62. Design a Flash Sale System
Sell 10,000 units to a million people at noon with a lottery waiting room, a Redis gate before an Aurora ledger and holds that expire.
ClassicMedium
Caching Databases Concurrency
+6
Aurora AWS Flash sale Inventory Redis Waiting room
Worked design
Practice
88. Design a Reviews and Ratings System
Dish reviews only from customers who ordered them, votes counted from a change stream, reviews ranked by the Wilson bound, payouts made exactly once.
ClassicMedium
Databases Streaming Distributed systems
+7
AWS DynamoDB Kafka Ranking Ratings Reviews Social
Worked design
Practice
89. Design a Donations Website for a Charity Event
Ten charities, three days, $100 M: charge through a third-party processor exactly once, queue the broadcast spikes, keep live totals on sharded counters. One-hour boards for junior, senior and staff, with the theory behind them.
ClassicMedium
Sharding Queues Databases
+6
Distributed systems AWS DynamoDB Idempotency Payments Reconciliation
Worked design
Practice
90. Design a Book Seller Aggregator Platform
Buy the cheapest offer under a maximum price from 1,000 sellers: cached offers, coalesced quotes, a hold-order-capture saga, open requests.
ClassicMedium
Caching Databases AWS
+5
Booking DynamoDB Marketplace Payments Sagas
Worked design
Practice
92. Design Online Chess
Real-time rated chess with server-validated moves, lag-compensated clocks, pairing by rating and a million watchers on one game.
ClassicMedium
Databases AWS DynamoDB
+4
Gaming Matchmaking Ratings WebSockets
Worked design
Practice
93. Design a Real-Time Game Leaderboard
Rank 200 million players in real time with sharded Redis sorted sets, count every game exactly once, and close a season fairly.
ClassicMedium
Caching Databases Streaming
+8
Distributed systems AWS Flink Gaming Kafka Leaderboards Redis Sorted sets
Worked design
Practice
95. Design a Team Chat App like Slack
Design a team chat app like Slack: channels and DMs in real time, threads, unread counts and search. One-hour boards for junior, senior and staff, with the theory behind them.
ClassicMedium
Databases Search AWS
+5
DynamoDB Fan out Messaging Real time WebSockets
Worked design
Practice
99. Design a Cross-Product Tagging System
One set of tags across Jira issues, Confluence pages and Bitbucket pull requests: batch renders, tag pages that never leak, suggestions, popular tags.
ClassicMedium
Databases Search Security
+6
AWS Collaboration DynamoDB Many to many OpenSearch Permissions
Worked design
Practice

Each design brings together the brief, practice, examples and discussion.