Learn computer science by building things
An interactive textbook where theory and practice happen in the browser. Unlock domains like levels: networking, operating systems, security, data and more.
Domains
Start free
These entry nodes are free. No account needed to begin.
Frequently asked questions
Is it free?
Yes. The first level of every subject is free and needs no account. Deeper levels and the senior grades are paid — that is what keeps the project running.
What age is this for?
It is written for curious teenagers from about 12 and for adults starting from zero. Nothing assumes prior programming experience; lessons about networking and physics need no mathematics beyond school level.
Do I need to know programming already?
No. The logic, physics and networking tracks start from nothing. The languages track is where you actually write code, and it also starts from the beginning.
Do I need to install anything?
No. Everything runs in the browser: theory, practice and the interactive simulations. There is nothing to download and no environment to configure.
How long does one subject take?
A lesson takes 10 to 15 minutes. A junior grade is roughly 12 to 20 lessons, so expect a few weeks of steady practice rather than one evening.
Do I have to follow the order?
Within a grade, levels open one after another, because each builds on the previous one. Between subjects you are free: start with logic, physics or networking.