A bank of practice prompts to test yourself with. The 36 case studies are your worked examples; this is your exam. Some problems here are fully worked (novel designs not in the case studies); the rest is a large prompt list — attempt each cold, then check yourself against the rubric or the linked case study.
How to use: pick a problem, set a 45-minute timer, design it cold and out loud following the framework, then grade yourself with the self-grading checklist. Space your redos (see how to practice).
These come with a solution so you can calibrate on problems you haven’t already read:
| # | Problem | Twist it tests |
|---|---|---|
| 1 | Design a Digital Wallet | Balance correctness, idempotent transfers, ledger |
| 2 | Design a Coupon / Discount Service | Redemption limits under concurrency, abuse |
| 3 | Design an Online Judge (LeetCode) | Sandboxed untrusted code execution at scale |
| 4 | Design a Live-Streaming Comments System | Real-time fan-out to millions of viewers |
Design: an email service (Gmail) · a calendar (Google Calendar) · a code-hosting service (GitHub) · a music streaming service (Spotify) · a Q&A site (Quora/Stack Overflow) · a delivery-tracking system · a URL/website uptime monitor · a distributed lock service · a CDN · a DNS system · an OAuth/SSO service · an A/B testing platform · a comment system · a “nearby friends” feature · a photo-sharing app · a video-conferencing service (Zoom) · a search-suggestions ranking system · a shopping cart service · a subscription-billing system · a content-moderation pipeline.
🚨 For the extra prompts, you won’t find a write-up — that’s the point. By now you should be able to derive them from the recurring patterns. If you can design “Spotify” by recognizing it’s Instagram’s media pipeline + a recommendation system, you’ve got it.