A cozy pixel-art game that teaches Rust from the ground up.
25 islands · 187 levels · the whole Rust Book · a real compiler · and Ferris the crab as your teacher, powered by Claude.
You need Rust (the game compiles your code with your own rustc). For Ferris to talk, you also need Claude Code; without it, switch Ferris to offline mode in Settings and he gives built-in hints. Neovim is optional, for Vim mode.
git clone https://github.com/wanikhawar/ferris-forge
cd ferris-forge
cargo runYour browser opens the game at http://127.0.0.1:7878. Press Ctrl+C in the terminal to quit.
The link the game opens (and prints in the terminal) ends in #key=…. The game runs Rust code and Neovim for whoever uses its API, so the API only answers pages that have this key; other programs and other users on your computer can't. Your browser remembers it, so later you can just open http://127.0.0.1:7878. In a new browser or a private window, use the printed link once. The key is kept in save/game.key, readable only by you; delete that file to make a new one.
Developed and tested on Linux.
 The world map. 25 islands, each a part of the Rust Book. Clear an island's boss to unlock the next. |
 A level. Code on the left, Ferris on the right. Hints, explanations and code reviews come from Ferris. |
 Real results. Your code is compiled and run with rustc, and checked by its output or by Ferris' tests. |
 Lessons. A short lesson for every level, with how it compares to C and Python, and a link to the book. |
 Vim mode. Edit with your own Neovim and your own config, running invisibly behind the editor. |
 Ferris has moods. He thinks while you compile, worries when it breaks, and dances when it works. |
- Real compiler. Your code is compiled and run with your own
rustc. The compiler and tests decide whether you pass a level, not the AI. - Ferris = Claude. Explanations, hints, code reviews and chat go through
claude -p(Claude Code's headless mode), so they use your Claude subscription. There's no API key. Ferris has no tools in the game: he can only talk. - Switch models with the 🧠 chip under Ferris (Fable, Opus, Sonnet, Haiku, or any model name Claude Code accepts) and pick an effort level.
- The ⚡ "E" bar in the top-right corner shows how much of your Claude usage limit is left. It updates after Ferris answers.
- Offline mode (in Settings) uses built-in hints and doesn't touch your Claude limit.
🔧 Fix it: broken code to repair · ✍️ Fill it: write the missing part · 🔮 Predict it: guess the output · 📖 Quiz: a concept question · 👹 Boss: a mini-project at the end of each world.
Levels can also give your program keyboard input, command-line arguments, environment variables and extra files (see the stdin, args, env and files fields in the level TOML).
Hints cost XP on that level (−10%, −30%, then −60% for the full answer). If Ferris' code review says your passing code is idiomatic, you get +15 bonus XP.
Click VIM above the editor (or turn it on in Settings) and every keystroke goes to your own Neovim, running invisibly in the background (nvim --embed). Motions, operators, text objects, registers, macros, :s, undo and your keymaps all work. The status line under the code shows the mode and your : commands.
- By default it loads your config (
~/.config/nvim). Settings can switch to a clean Neovim instead. - It never writes files: the buffer is a scratch buffer, and the game saves your code itself.
- Use Ctrl+Shift+C / Ctrl+Shift+V for the system clipboard. Some browser shortcuts (like Ctrl+W) can't be captured by a web page.
| Key | Action |
|---|---|
| Ctrl+Enter | Run your code |
| 1–9, N | Hotbar: Run, Compiler, Output/Results (with the Expected or Tests tab), Hint, Explain, Review, Reset, Skip, Map, Next |
| A–D | Answer a predict question |
| Tab / Shift+Tab | Indent / dedent |
| Ctrl+/ | Toggle comment (when Vim mode is off) |
| L | Open the lesson |
| Q | Quick questions for Ferris |
The curriculum follows The Rust Programming Language, using Brown University's interactive edition (https://rust-book.cs.brown.edu). The 25 islands cover the whole book, ordered by what you need to know first rather than by chapter number. levels/book.toml lists every chapter and section; each level says which sections it teaches, and the lesson popup links straight to them.
| # | Island | Book |
|---|---|---|
| 0 | Tutorial Beach | Ch 1, 3.4 |
| 1 | Variable Village | 3.1–3.2 |
| 2 | Flow Forest | 3.3, 3.5 |
| 3 | Ownership Caves | 4.1 |
| 4 | Borrow Bridge | 4.2–4.5 (incl. the permissions model, fixing ownership errors) |
| 5 | Struct Smithy | Ch 5 |
| 6 | Enum Isles | Ch 6 (+ Ownership Inventory #1) |
| 7 | Collection Citadel | Ch 8 (+ Inventory #2) |
| 8 | Error Marsh | Ch 9 |
| 9 | Guessing Game Grotto 🛠 | Ch 2 (project) |
| 10 | Pattern Plains | Ch 19 |
| 11 | Module Mines | Ch 7 |
| 12 | Testing Grounds | Ch 11 |
| 13 | Trait Tower | 10.1–10.2, App. C |
| 14 | Lifetime Labyrinth | 10.3 (+ Inventory #3) |
| 15 | Iterator Rapids | 13.1, 13.2, 13.4 |
| 16 | Minigrep Harbor 🛠 | Ch 12, 13.3 (project) |
| 17 | Pointer Peaks | Ch 15 |
| 18 | Object Observatory | Ch 18 (+ Inventory #4) |
| 19 | Thread Volcano | Ch 16 |
| 20 | Async Archipelago | Ch 17 |
| 21 | Cargo Docks | Ch 14 |
| 22 | Advanced Abyss | Ch 20 |
| 23 | Web Server Citadel 🛠 | Ch 21 (final project) |
| 24 | Ferris' Library 📚 | Appendices |
Levels are compiled with plain rustc, so they can't use crates. The Async Archipelago levels therefore come with runtime.rs, a tiny async runtime built from the standard library (block_on, sleep, join, race, channels and streams) that stands in for tokio or the book's trpl. The Web Server Citadel tests act as browsers over real TCP connections on 127.0.0.1.
src/ Rust backend (axum): runner (rustc), teacher (claude -p), Vim bridge, progress, API
levels/ the curriculum: one TOML file per world, plus book.toml (the book's contents)
web/ the pixel UI (plain HTML/CSS/JS, no build step)
docs/ the README's images; docs/art/make-art.html redraws its artwork
save/ your progress (created on first run)
To check that every level is solvable (each starter fails, each solution passes, each predict answer is correct):
cargo run -- verify # every world
cargo run -- verify 5 # just world 5cargo run -- verify also checks coverage: every book topic must be taught by at least one level, and every section id a level mentions must exist.
The game runs on your own computer and only listens on 127.0.0.1. It runs the code you write (as you, like cargo run would), so be as careful with code pasted from elsewhere as you would be in a terminal.
- Only the game's own page can use its API (see the key above); other websites and other local programs can't.
- Each program runs with limits on memory, file size and CPU time, and is stopped after 5 seconds. On Linux it runs in its own process namespace, so nothing it starts outlives the run.