Challenges
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Build your own Shell
Learn about parsing shell commands, executing programs and more
FREE THIS MONTH
This challenge is free until 1 November 2026!
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Build your own Redis
Learn about TCP servers, the Redis protocol and more
124 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.
25 stages
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.
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Language Tracks
Rust
Popular
This track is a favourite among our learners.
412 stages
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Go
Popular
This track is a favourite among our learners.
412 stages
Start
Python
Popular
This track is a favourite among our learners.
412 stages
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C
412 stages
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C#
412 stages
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C++
412 stages
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Clojure
231 stages
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Crystal
124 stages
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Dart
214 stages
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Elixir
366 stages
Start
Gleam
372 stages
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Haskell
357 stages
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Java
412 stages
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JavaScript
412 stages
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Kotlin
399 stages
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OCaml
305 stages
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Odin
331 stages
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PHP
355 stages
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Ruby
374 stages
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Scala
342 stages
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TypeScript
412 stages
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Zig
412 stages
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