Commands

The faber CLI, as a command index. For flags and compiler pipeline detail, open The faber CLI.

Daily loop#

Command	Use it for
`faber check <package>`	Fast front-end validation: lex, parse, type check, lower
`faber build <package> -t rust`	Emit a Rust project for review or native compilation
`faber run <package>`	Build and execute an application package
`faber test <package>`	Run package tests when the package defines test surfaces
`faber explain <code>`	Read a stable diagnostic explanation

Start with check. It is the cheapest command and the one agents should run before proposing generated code as valid Faber.

Check#

faber check .
faber check examples/ai-workbench/packages/faber-ai

A passing check means the package is syntactically and semantically acceptable to the compiler front end. It does not mean the final native toolchain has been invoked.

Build#

faber build . -t rust

The Rust target is intentionally reviewable. Generated Rust is a compiler artifact, not source of truth; edit the Faber package and rebuild rather than patching emitted Rust by hand.

Run#

faber run .

Use run for application packages with an main entry point. Library-only packages should be checked and tested instead.

Explain diagnostics#

faber explain SEM001
faber explain LEX006

Diagnostic families are stable handles: LEX for lexical errors, PAR for parser errors, SEM for semantic/type errors. In docs and agent reports, cite the diagnostic code instead of paraphrasing a compiler failure loosely.

Reader-locale commands#

faber format --locale=la path/to/file.fab
faber format --locale=th-TH path/to/file.fab
faber emit -t faber --locale=zh-Hans path/to/file.fab

Reader locale output is a rendering of the compiler's semantic model, not a browser-time translation layer. Locale work belongs after a package checks in canonical form.

Device execution#

Packages carrying an @ nucleum compute kernel run on a GPU. Backend selection is explicit and fail-closed — a named backend never silently falls back to CPU.

faber run --backend metal <package>
faber run --backend cuda <package>
faber run --backend auto <package>

See device execution for the contract.

Related: Cheat sheet · Testing · Hello, Faber