Only

A task language for explicit, cross-platform workflows.

Usage guide Complete example VS Code extension

Quick start

An Onlyfile describes tasks and their execution stages:

!version 0.4
!var pnpm_dir = "web"

# Internal setup task.
[fail] Preparation failed
_prepare():
    | cd {{pnpm_dir}}
    | pnpm install
    cargo fetch

[help] Run CI
[pass] CI complete
ci()
    & _prepare
    & (front.check, back.check)
    & (front.test, back.test)
:

[help] Frontend checks
[desc] The pnpm dir is {{pnpm_dir}}/
group front {

    check():
        pnpm --dir {{pnpm_dir}} lint

    test():
        pnpm --dir {{pnpm_dir}} test
}

[help] Backend checks
group back {

    check():
        cargo check

    test() ? @has("cargo-nextest"):
        cargo nextest run

    test():
        cargo test
}

& advances to the next dependency stage; tasks inside ( ... ) run in parallel.

Run only to list tasks, or run one directly:

only
only ci

Inspect the resolved workflow before running it:

only ci --dry-run --full

Dry run: ci()
├─ stage 1
│  └─ _prepare
│     ├─ block (deno)
│     │  ├─ cd web
│     │  └─ pnpm install
│     └─ cargo fetch
├─ stage 2 (parallel)
│  ├─ front.check
│  │  └─ pnpm --dir web lint
│  └─ back.check
│     └─ cargo check
├─ stage 3 (parallel)
│  ├─ front.test
│  │  └─ pnpm --dir web test
│  └─ back.test
│     └─ cargo nextest run
└─ stage 4
   └─ ci

Format the file with:

only --fmt

The workflow structure stays in the task definition instead of being hidden in shell control flow. See the usage guide for parameters, guards, shells, command blocks, and groups.

Why Only

• Explicit stages — & expresses order and ( ... ) expresses parallelism.
• Structured tasks — parameters, guards, groups, helpers, and metadata are part of the language.
• Cross-platform commands — use the built-in shell by default, or select a host shell when needed.
• Inspectable workflows — the formatter, diagnostics, editor tooling, and --dry-run --full understand the same task graph.

Compared with just and Task

just, Task, and Only can all run project commands. Only focuses on making execution stages and parallel groups explicit in the task definition.

Install

macOS / Linux

curl -fsSL https://raw.githubusercontent.com/KercyDing/only/master/install.sh | sh

Windows PowerShell

irm https://raw.githubusercontent.com/KercyDing/only/master/install.ps1 | iex

Cargo

cargo install only

Arch Linux

paru -S only-bin

For the latest Git version:

paru -S only-git

GitHub

cargo install --git https://github.com/KercyDing/only only

Update

only --upgrade

or:

only --update

License

MIT