@fabycode/cli

Faby — the AI-native programming language, designed end-to-end by Claude Fable-5. Token-minimal · deterministic · one canonical form.

npm i -g @fabycode/cli

Quick start

faby init hello && cd hello
faby run main.fy

Hello, World — welcome to Faby.
Hello, Fable-5 — welcome to Faby.
Hello, you — welcome to Faby.

What is Faby?

Faby is the first programming language conceived end-to-end by an AI model — built for the era in which code is generated, reviewed and maintained by machines, and verified by humans.

flow fib(n: Int) -> Int
  match n
    0 | 1 -> n
    _     -> fib(n - 1) + fib(n - 2)

flow main
  range(1, 50)
    |> filter(_ % 3 == 0)
    |> map(_ * _)
    |> take(5)
    |> each(print)

• Flows, not functions — the last expression returns, no ceremony
• Pipelines — data reads left to right with |>
• Exhaustive match — the compiler-grade runtime rejects missed cases
• Contracts — expect / ensure are part of the signature and actually fail
• Recovery operators — ? default(x), ? retry(3), ? skip, ? fail at the call site

Commands

| Command | Description | | --- | --- | | faby run <file.fy> | run a program (--json for machine-readable output) | | faby repl | interactive session with persistent state | | faby init [name] | scaffold a new project | | faby version | print version | | faby help | help |

Scope of this release

This is the Genesis runtime (v0.1): the same interpreter that powers the browser playground, packaged for your terminal. It covers flows, recursion, pipelines with _-lambdas, exhaustive pattern matching with guards, contracts and recovery operators, plus ~20 stdlib builtins.

The full native toolchain — faby build, faby check --intent, spawn concurrency, semantic types — ships with v0.2 "Pulse". Follow the roadmap at faby.codes.

Links

• Website: faby.codes
• Language docs: faby.codes/docs
• CLI reference: faby.codes/cli
• Playground: faby.codes/playground
• X / Twitter: @fabylanguage

MIT © 2026 The Faby Project · Designed by Claude Fable-5