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 June 2026!
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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.
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.
396 stages
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Go
Popular
This track is a favourite among our learners.
396 stages
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Python
Popular
This track is a favourite among our learners.
396 stages
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C
396 stages
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C#
396 stages
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C++
396 stages
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Clojure
222 stages
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Crystal
115 stages
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Dart
90 stages
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Elixir
350 stages
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Gleam
356 stages
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Haskell
348 stages
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Java
396 stages
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JavaScript
396 stages
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Kotlin
390 stages
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OCaml
296 stages
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Odin
322 stages
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PHP
337 stages
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Ruby
365 stages
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Scala
333 stages
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TypeScript
396 stages
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Zig
396 stages
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