3 live · 9 locked
Pick a system
01 · URL Shortener
KGS ranges + base62 + hash-shard. Watch a shorten mint without coordination, then a redirect hit the cache.
12 min · Starter →
02 · Rate Limiter
Token bucket in one Redis Lua eval. Fire a burst, see 429s land, flip to sliding-window and compare.
10 min · Core →
03 · Twitter Timeline
Hybrid fan-out at 1.2M deliveries/s. Hit the World-Cup-final button and watch the celebrity playbook engage.
15 min · Advanced →
News Feed
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
WhatsApp Chat
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
YouTube
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
Uber & Lyft
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
Web Crawler
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
Search Autocomplete
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
Notification System
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
Distributed KV
Locked — votes decide build order. Pro members get all 12 + mock-interview mode.
🔒 pro
How to use these
Press Step before you read
Each flow is steppable: Play runs the request, Step advances one idea (one packet hop), Reset clears. Solid arrows are sync (you wait); dashed arrows are async (fire-and-forget). Drag nodes to untangle, toggle 301/302, hit/miss, celebrity/normal, then drag the capacity sliders and watch QPS, storage and p99 move. Finish the quiz to mark the case complete — progress saves locally.
Theory lives in the garden: High Level Design track. Playgrounds are the lab; notes are the textbook.
Monetisation
HLD Pro — all 12 systems + interview mode
What Pro unlocks coming soon
All 12 case playgrounds, export-to-PNG architecture diagrams, timed mock-interview mode (45-min clock + follow-up questions), and copy-paste capacity sheets for your own interviews. Early supporters lock founding pricing.