Watch tutorials.
Ship working systems.
Rebuild Redis, Git, a database, an OS kernel — from an empty file to passing tests. Your code runs against a real executor, and it either passes or it doesn’t.
Free forever · no credit card · first test passing in ~2 minutes
# Frame a value as a RESP bulk string def encode_bulk(val): if val is None: return b"$-1\r\n" data = val.encode() return b"$%d\r\n%s\r\n" % (len(data), data)
Pick your first build
Twelve of the 179. Every one starts from an empty file and ends with yours working.
Build Redis
A server the real redis-cli can talk to.
Build a Database
B-tree pages, SQL parser, WAL recovery.
Build Git
Object store, index, diffs, real merges.
Build a Programming Lang
Lexer to bytecode VM to garbage collector.
Build a Container Runtime
Namespaces, cgroups — Docker without Docker.
Build a Shell
fork/exec, pipes, redirection, job control.
Build an OS Kernel
Boot sector to scheduler to userland.
Build a 3D Renderer
A rasterizer: meshes, shading, camera.
Build a Neural Network
Backprop by hand — no PyTorch allowed.
Build BitTorrent
Trackers, peer protocol, real .torrents.
Build a Load Balancer
Health checks, algorithms, live proxying.
Build a Raft KV Store
Consensus that survives kill -9.
Or follow a career path
Courses sequenced into a route — you see where it starts and what you’ll ship at the end before you commit an hour.
Backend Engineer
The infrastructure under every web service — Go, SQL, caches, queues, and the protocols that connect them.
Finish a course.
Get proof. Free.
Every completed course issues a certificate — and it’s only issued when every graded exercise has passed on the executor. Nothing to buy at the finish line.
- ✓LinkedIn-ready. A public verification page with a credential ID — one click adds it under Licenses & Certifications.
- ✓Lives in your GitHub README. Work in your own editor and your repo’s badge shows live progress — then turns into the certificate when you finish.
- ✓Means something. It certifies passed tests, not watched videos — the same bar for everyone.
You can’t cheat here. Your code either passes the tests or it doesn’t.
Teach or research? Peer-review a course.
We invite academics to review our curriculum — correct it, deepen it, and get credited on the course itself: your name, title, and institution, plus a verifiable Certificate of Peer Review.
The first test you make pass takes about two minutes.
Start building — it’s freeFree forever · no credit card · 179 courses · free certificates