Challenges
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Build your own Shell
Learn about parsing shell commands, executing programs and more
69 stages
Build your own Redis
Learn about TCP servers, the Redis protocol and more
115 stages
Build your own grep
Learn about regex syntax: character classes, quantifiers and more
33 stages
Build your own Interpreter
Learn about tokenization, ASTs, tree-walk interpreters and more.
84 stages
Build your own BitTorrent
Learn about .torrent files, the BitTorrent Peer Protocol and more
19 stages
Build your own Kafka
Learn about TCP servers, the Kafka wire protocol and more.
FREE DURING BETA
This challenge is free to try when it's in beta. We keep challenges in beta for a few weeks to gather feedback.
Start
Build your own Git
Learn about git objects, plumbing commands and more
7 stages
Build your own SQLite
Learn about SQL syntax, SQLite's file format, B-trees and more
9 stages
Build your own DNS server
Learn about the DNS protocol, DNS record types and more.
8 stages
Build your own HTTP server
Learn about TCP servers, the HTTP protocol and more
14 stages
Build your own Claude Code
Learn about LLM APIs, tool calling, agent loops and more
FREE DURING BETA
This challenge is free to try when it's in beta. We keep challenges in beta for a few weeks to gather feedback.
Start
Language Tracks
Rust
Popular
This track is a favourite among our learners.
389 stages
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Go
Popular
This track is a favourite among our learners.
389 stages
Start
Python
Popular
This track is a favourite among our learners.
389 stages
Start
C
364 stages
Start
C#
389 stages
Start
C++
389 stages
Start
Clojure
222 stages
Start
Crystal
115 stages
Start
Dart
83 stages
Start
Elixir
310 stages
Start
Gleam
349 stages
Start
Haskell
257 stages
Start
Java
389 stages
Start
JavaScript
389 stages
Start
Kotlin
375 stages
Start
OCaml
268 stages
Start
Odin
301 stages
Start
PHP
301 stages
Start
Ruby
241 stages
Start
Scala
184 stages
Start
TypeScript
389 stages
Start
Zig
381 stages
Start