Homebrew
macOS and Linux
Install from the SmartCrab tap.
brew install smartcrabai/tap/yabumiBrowse documentation
Single-file language for Agent Skills
Scripts agents can get right the first time.
Yabumi replaces fragile bash and oversized Python helpers with one typed, self-contained file. Effects, failures, mutability, and concurrency stay visible in the source.
# Fetch two manifests concurrently. Effects stay visible.
def manifest(url: str): Result[str, Error] uses {net}
response = http.get(url)?
return response.body
urls = ["https://api.example.com/a", "https://api.example.com/b"]
results = urls.par_map((url) => manifest(url))
results.each((result) => print(result.unwrap_or("failed")))1 fileScript and types travel together
0 depsSingle native binary distribution
6 effectsfs · net · env · proc · time · rand
4 commandsrun · check · test · lsp
Install
One binary. No runtime setup.
Choose Homebrew or the shell installer. Both install the ybm command.
Shell installer
Latest release
Download the platform binary from GitHub Releases.
curl --proto '=https' --tlsv1.2 -LsSf \
https://github.com/smartcrabai/yabumi/releases/latest/download/yabumi-installer.sh | shAgent Skill: install the bundled skill with npx skills add smartcrabai/yabumi --skill yabumi.
Quick start
From empty file to checked script.
Create hello.ybm
Top-level code runs from top to bottom. No entry-point ceremony.
name = env.get("USER").unwrap_or("agent")
print(f"hello, {name}")Check before execution
Type checking, formatting diff, lint, and doc-test type checking run together.
$ ybm check hello.ybmRun only after a clean check
ybm always type-checks first, then executes on success.
$ ybm hello.ybm
hello, agentLanguage model
What you see is what happens.
Yabumi removes the invisible behavior that makes generated scripts hard to audit. Four rules carry most of the language.
State
Immutable by default
Reassignment requires var. The first binding fixes the type.
x = 5
var retries = 0
retries = retries + 1
Auditability
Effects in every signature
Pure is the default. Filesystem, network, environment, process, time, and random access must be declared.
def save(path: str, body: str): Option[Error]
uses {fs}
Failure
Typed errors, explicit propagation
Result and Option cannot be silently ignored. ? returns failure early.
n = input.parse_int()?
return n * 2
Concurrency
Parallel only when written
par, par_map, and par_each make fan-out visible and preserve input order.
pages = urls.par_map((url) =>
http.get(url))
CLI reference
Four commands, one diagnostic format.
Every failure uses file:line:col [E0000] message. Stable error codes let agents recover without parsing prose.
| Command | Behavior | Success |
|---|---|---|
ybm <file> | Type-check, then run only on success. | Exit 0 |
ybm check | Type-check, read-only format diff, lint, and doc-test type checking. | Clean file |
ybm test | Execute fenced examples in declaration doc comments. | All pass |
ybm lsp | Start the Language Server Protocol server over stdio. | Clean shutdown |
Use ybm check --apply <file> to rewrite formatting in place. Without --apply, formatting stays read-only.
Standard library
Useful without imports.
Core types and namespaces are globally available. Effectful functions declare the same effect vocabulary as user code.
jsoncsvyamltomlfshttpenvproctimerandregexmath
Safe and direct APIs coexist. Indexing may terminate on an invalid key; .get() returns Option. The choice stays visible at the call site.
Editor support
Diagnostics while you write.
ybm lsp speaks LSP over stdio and analyzes open files without executing them.
Feedback
Live diagnostics
Parse, type, effect, and lint errors use the same stable diagnostic codes as the CLI.
Navigation
Language-aware editing
Live diagnostics, type hover, go to definition, and whole-document formatting over full-document synchronization.
Full reference
Go deeper without losing the source of truth.
The language specification is canonical. Decisions record resolved design details; verified samples double as acceptance tests.