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
FREE THIS MONTH
This challenge is free until 1 May 2026!
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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.
389 stages
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Go
Popular
This track is a favourite among our learners.
389 stages
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Python
Popular
This track is a favourite among our learners.
389 stages
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C
389 stages
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C#
389 stages
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C++
389 stages
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Clojure
222 stages
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Crystal
115 stages
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Dart
83 stages
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Elixir
343 stages
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Gleam
349 stages
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Haskell
341 stages
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Java
389 stages
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JavaScript
389 stages
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Kotlin
383 stages
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OCaml
289 stages
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Odin
315 stages
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PHP
322 stages
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Ruby
358 stages
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Scala
326 stages
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TypeScript
389 stages
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Zig
389 stages
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