Practice system design
Draw a Design on a typed canvas, run Operations through it step by step, then inject a Fault and watch which Checks still pass. 13 Exercises in 3 Tracks, built for engineers preparing for system design interviews.
Load Balancers, Services, databases and queues on a typed canvas: a Connection must make sense.
Send Operations through your Design and follow each step, with the numbers from the Exercise’s scale.
Kill a Component or lose a response, and see which of the Exercise’s Checks your Design still passes.
The building blocks every design reuses: durable writes, caching, and work done off the hot path.
Billions of unique codes, redirects at scale, and a disabled link that actually stops.
A Stripe-style API limit: 100 requests a minute per key, counted once across every machine.
A Twitter-style feed: post once, reach every follower, and keep the feed fast for people who only scroll.
Login codes that never wait behind a campaign, providers that fail, and an SMS that must not go out twice.
Coming soon. Open the app to get an email when it arrives.
Seats two people want at once, money that must add up, agents and jobs that must act once, partners that fail, and leaders that come back after losing their majority.
A Ticketmaster-style on-sale: hold seats, charge once, and give the seat back when nobody pays.
A wallet that moves money between accounts and out to a bank: a ledger that always adds up, and a bank that fails.
AI agents turn tickets into pull requests: one agent per task, one PR per task, proof before review.
A cron-style service: run millions of jobs on time, once, while workers pause and come back.
Thousands of bids a second on one item, one winner, and a leader that comes back after losing its majority.
Big files, live updates and many devices that must agree on what changed.
Big files that go straight to storage, and a change on your laptop that reaches your phone in seconds, never skipped.
Messages that arrive in a second, survive a dropped connection, and never show twice.
One goal, ten million screens a second later: each play sent once, counted once, never skipped.
A YouTube-style service: upload, transcode and play millions of videos, while workers die and come back late.
The URL Shortener Exercise and the Sandbox. No account needed: your work stays on your device.
Every Exercise, with its Checks and Fault Drills, and every new one as it arrives.