Build the system. Survive the day. See why it held.

Learn by making a design work

Clarify the brief, estimate the scale and connect the parts. Fast-forward through a traffic day, then use the plain-words debrief to compare reliability, speed, data safety and monthly cost. Playing on this site needs a free Google or GitHub account. Rather run it yourself? The code is open source (MIT) and runs with no account.

Browse the practice problems, read the lessons or follow a guide before you play.

Start here

• Your first system
• URL shortener practice
• How to practise system design
• A two-week interview plan

Common questions

What is System Designer?

A free browser game for learning system design. Build an architecture, run a simulated traffic day of spikes and outages, and see how it handles reliability, speed, data safety and cost.

Who is it for?

Backend engineers, students and interview candidates who want to understand how systems behave. Beginners can start with the guided first system; experienced engineers can try harder constraints.

Is it free?

Yes. The lessons, practice problems and sandbox are free.

Does it need an account?

On systemdesigner.io, yes: a free account with Google or GitHub is needed to play. Reading the problems, lessons and guides needs no account. The code is open source (MIT), so you can also run your own copy with no account at all.

Does it help with interviews?

It helps you practise clarification, estimates, architecture, failures and trade-offs. Interview mode on Medium and Hard problems adds a timed discussion and evidence-based defenses.

How is it different from reading a book?

You make a prediction and watch your own design face traffic and failures. A debrief gives measurements for a retry. Books can explain the ideas; playing makes you apply and test them.