Units 0 and 1 are free, forever

System design, one building at a time. Then keep it standing.

Learn system design in 10 minutes a day. Every lesson adds a building to your city. Watch requests drive between them, predict what breaks, and learn the fix before the next district opens.

Or try a free lesson now.

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How a lesson works

  1. 1. Watch 3 minutes

    A narrated animation shows the idea moving: requests flowing, caches filling, servers catching fire. Prefer reading? Every lesson has a full read mode.

  2. 2. Answer as you go

    The lesson pauses to ask you. Every answer, right or wrong, explains why.

  3. 3. Remember it for good

    Key ideas become flashcards that come back right before you'd forget them.

  4. 4. Keep the streak

    A daily goal that takes 10 minutes, with streak freezes for busy days.

  5. 5. Practice the interview

    Design drills and mock interviews with feedback on your own answers.

Your course is a map.

Each district is a unit: 13 of them, from "what is a server" to designing a ride-hailing app. Finish a district's lessons and its lights come on.

  1. District 0 · Open

    Start hereFree

    What system design is, how to approach a design question, and the numbers every engineer should know.

  2. District 1 · Open

    How the web talksFree

    DNS, HTTP, TCP and UDP, API styles, and real-time connections.

  3. District 2 · Open

    Scale basics

    Scalability, latency and throughput, horizontal scaling, availability.

  4. District 3 · Open

    Traffic management

    Load balancers, reverse proxies, CDNs, API gateways and rate limiting.

  5. District 4 · Open

    Caching

    Where to cache, caching strategies, eviction and invalidation.

  6. District 5 · Open

    Data storage

    SQL and NoSQL, indexes, replication, sharding, blob storage and IDs.

  7. District 6 · Coming soon

    Async & messaging

    Queues, pub/sub, logs, delivery guarantees and back pressure.

  8. District 7 · Coming soon

    Distributed systems

    CAP, consistency models, quorums, consensus and distributed transactions.

  9. District 8 · Coming soon

    Architecture styles

    Monoliths, microservices, event-driven systems, CQRS and serverless.

  10. District 9 · Coming soon

    Search & special data structures

    Inverted indexes, tries, Bloom filters and geospatial indexes.

  11. District 10 · Coming soon

    Reliability & operations

    Observability, retries, circuit breakers, antipatterns and disaster recovery.

  12. District 11 · Coming soon

    Security essentials

    Authentication, authorization, tokens, encryption and secrets.

  13. District 12 · Coming soon

    Cloud design patterns

    Reusable patterns for messaging, data, migration and resilience.

Enter the city

13 districts · Open now

System Design

Networking, caching, databases, queues and distributed systems, then full case studies like a URL shortener and a ride-hailing app.

Start the course

17 districts · 152 lessons · Coming soon

AI Engineering

From your first model API call to RAG, agents, evals and serving models yourself, with every buzzword explained in plain words.

See the plan

Keep the lights on.

Learn or review for about 10 minutes a day and your streak grows. Busy day? A saved streak freeze keeps the lights on until you're back.

Simple pricing

One-time payments, no subscriptions. Prices adjust automatically in many countries.

Free

$0

Forever

  • Start here + How the web talks
  • One taster lesson from Caching
  • Daily flashcards and streaks for free lessons
  • A design drill

3 months

$29

One-time, no auto-renew

  • Every lesson and case study
  • AI feedback on design answers
  • Mock interviews
  • Exam-date study plan

Lifetime

$49$79

Early-bird, one-time

  • Everything in 3 months
  • All future lessons and case studies

Questions

Who is this for?

Engineers preparing for system design interviews, developers who want to understand the tools they use, and students who find the usual resources overwhelming.

Do I need to know distributed systems already?

No. Unit 0 starts from what a server is. Experienced engineers can test out of early units.

How long does it take?

About 10 minutes a day. Most people cover the core units in 6 to 8 weeks.

Is the free plan really free?

Yes, with no time limit. The first two units, a taster lesson and a design drill are free forever.

Get early-bird access

Join the waitlist and get lifetime access at the early-bird price when we open.