01 · DECIDE
Make the call
Sort features into what version 1 needs and what waits, put the steps of a request in order, or pick the fix. Drag the cards, or tap them.
SYSTEM DESIGN · 140 INTERACTIVE LESSONS
Learn system design one decision at a time.
Each screen asks you to make one call, like what version 1 needs, how busy it gets, or what breaks first. You see right away if it holds, and the design grows from your answers.
✓ No code to write✓ First chapter free✓ Works on your phone
HOW A LESSON WORKS.
One decision
per screen.
About 10 screens a lesson. The design lessons go in the order of an interview: scope, data, API, the busy path, the numbers, then scale and the deep dives. A wrong answer tells you why before you try again.
02 · DRAW
Draw the design
Each answer adds to the diagram. In Design a URL Shortener you draw it yourself: add the parts, tap to connect them, and the check tells you what’s missing or doesn’t belong.
03 · CHECK
Do the numbers
Estimate the traffic, then see what breaks. Every lesson uses the same round numbers, like 5,000 lookups a second for one database server, so you learn to size things fast.
WHAT’S INSIDE.
From what a server is
to designing Uber.
Start with the ideas every design uses, then design the systems interviews ask about. The practice problems give you a new system with less help, once you’ve seen one like it.
FOUNDATIONS · FREE
How the web works
What happens when you open a link, APIs, latency, back-of-the-envelope numbers, scaling up or out, and the interview framework.
BUILDING BLOCKS
The parts every design uses
Load balancing, caching, CDNs, SQL or NoSQL, indexes, replication, sharding, consistent hashing, message queues, rate limiting and more.
ENGINEERING CRAFT
What makes it work in production
API versioning, pagination, API keys, idempotency, webhooks, transactions, retries and circuit breakers, monitoring, safe deployments and multi-region.
CLASSIC DESIGNS
The systems interviews ask about
A URL shortener, Twitter, chat, YouTube, Dropbox, a web crawler, Uber, Ticketmaster, a payment system, Google Docs, and AI systems like ChatGPT.
PRACTICE PROBLEMS · 2 FREE
Your turn
Pastebin, Image Hosting, Slack, Discord, Zoom, Pinterest, Stack Overflow and more.
THEN TRY IT AS AN INTERVIEW.
Same problem, with an AI interviewer.
Each design problem has a Practice as an interview button. An AI interviewer runs it as a real round: you take notes one step at a time, draw the parts on a board, answer its follow-ups, and get a scorecard at the end.
How mock interviews workWHAT’S INCLUDED.
Start free.
The first chapter is free with an account. Without one, you can still play the first few screens of any lesson.
FREE ACCOUNT
8lessons: the Foundations chapter, plus the Pastebin and Image Hosting practice problemsPRO
140lessons, all of them, along with the whole coding course in 11 languages and mock interviewsPRO starts with a 7-day free trial.
See pricingDo I need to know how to code?
No. There’s no code to write: you sort, order, pick and work out numbers. It helps to know roughly what a server and a database are, and the Foundations chapter starts there.
Is it for system design interviews?
Yes. The design lessons go in the order of an interview round, and The Interview Framework lesson teaches that order on its own. When you’re ready, practice the same problem with the AI interviewer.
Which course is it in?
All of them. System design is Part 4 of every language course on AlgoCademy, and it’s the same in each, because there’s no code in it.
Can I read it instead?
Every lesson also has a Written walkthrough tab: the whole design with the numbers and the trade-offs, for review before an interview.
What if I get stuck?
A wrong answer explains why. With an account, Get help on any screen asks the AI tutor about that screen.
Can I use it on my phone?
Yes. Tap a card and then the group it goes in, or hold and drag. To draw an arrow, tap one part and then the next. The diagrams fit the screen.
NO CARD NEEDED.
Start with what happens
when you open a link.
The first lesson is free, and you can start it without an account.
Foundations · Building blocks · Engineering craft · Classic designs · Practice