Just Command Runner

name description version

just-cli

This skill should be used when the user asks to "create a justfile", "write just recipes", "configure just settings", "add just modules", "use just attributes", "set up task automation", mentions justfile, just command runner, or task automation with just.

0.1.0

Just Command Runner

Overview

Expert guidance for Just, a command runner with syntax inspired by make. Use this skill for creating justfiles, writing recipes, configuring settings, and implementing task automation workflows.

Key capabilities:

Create and organize justfiles with proper structure

Write recipes with attributes, dependencies, and parameters

Configure settings for shell, modules, and imports

Use built-in constants for terminal formatting

Implement check/​write patterns for code quality tools

Quick Reference

Essential Settings

set allow-duplicate-recipes # Allow recipes to override imported ones set allow-duplicate-variables # Allow variables to override imported ones set shell := [ " bash" , " -euo" , " pipefail" , " -c" ] # Strict bash with error handling set unstable # Enable unstable features (modules, script attribute) set dotenv-load # Auto-load .env file set positional-arguments # Pass recipe args as $1, $2, etc.

Common Attributes

Attribute Purpose

[group("name")] Group recipes in just --list output

[no-cd] Don't change to justfile directory

[private] Hide from just --list (same as _ prefix)

[script] Execute recipe as single script block

[script("interpreter")] Use specific interpreter (bash, python, etc.)

[confirm("prompt")] Require user confirmation before running

[doc("text")] Override recipe documentation

[positional-arguments] Enable positional args for this recipe only

Multiple attributes can be combined:

[ no-cd , private ] [ group ( " checks" )] recipe : echo " hello"

Built-in Constants

Terminal formatting constants are globally available (no definition needed):

Constant Description

CYAN , GREEN , RED , YELLOW , BLUE , PURPLE Text colors

BOLD , ITALIC , UNDERLINE , STRIKETHROUGH Text styles

NORMAL Reset formatting

BG_* Background colors (BG_RED, BG_GREEN, etc.)

HEX , HEXLOWER Hexadecimal digits

Usage:

@ status : echo -e ' {{ GREEN }} Success! {{ NORMAL }} ' echo -e ' {{ BOLD + CYAN }} Building... {{ NORMAL }} '

Key Functions

Require executable exists (fails recipe if not found)

jq := require ( " jq" )

Get environment variable with default

log_level := env ( " LOG_LEVEL" , " info" )

Get justfile directory path

root := justfile_dir ()

Recipe Patterns

Status Reporter Pattern

Display formatted status during multi-step workflows:

@_ run-with-status recipe * args : echo " " echo -e ' {{ CYAN }} → Running {{ recipe }} ... {{ NORMAL }} ' just {{ recipe }} {{ args }} echo -e ' {{ GREEN }} ✓ {{ recipe }} completed {{ NORMAL }} ' alias rws := _run-with-status

Check/​Write Pattern

Pair check (verify) and write (fix) recipes for code quality tools:

[ group ( " checks" )] @ biome-check + globs = " ." : na biome check {{ globs }} alias bc := biome-check

[ group ( " checks" )] @ biome-write + globs = " ." : na biome check --write {{ globs }} alias bw := biome-write

Full Check/​Write Pattern

Aggregate all checks with status reporting:

[ group ( " checks" )] @ full-check : just _run-with-status biome-check just _run-with-status prettier-check just _run-with-status tsc-check echo " " echo -e ' {{ GREEN }} All code checks passed! {{ NORMAL }} ' alias fc := full-check

[ group ( " checks" )] @ full-write : just _run-with-status biome-write just _run-with-status prettier-write echo " " echo -e ' {{ GREEN }} All code fixes applied! {{ NORMAL }} ' alias fw := full-write

Standard Alias Conventions

Recipe Alias Recipe Alias

full-check fc full-write fw

biome-check bc biome-write bw

prettier-check pc prettier-write pw

mdformat-check mc mdformat-write mw

tsc-check tc ruff-check rc

test t build b

Inline Scripts

Just supports inline scripts in any language via two methods:

Script Attribute (Recommended)

Use [script("interpreter")] for cross-platform compatibility:

[ script ( " node" )] fetch-data : const response = await fetch( ' https://api.example.com/data' ); const data = await response.json(); console.log(data);

[ script ( " python3" )] analyze : import json with open( ' package.json' ) as f: pkg = json.load(f) print(f " Package: {pkg['name']}@{pkg['version']}" )

[ script ( " bash" )] deploy : set -e npm run build aws s3 sync dist / s3: // bucket /

Shebang Method

Use #!/​usr/​bin/​env interpreter at the recipe start:

node-script : #!/​usr/​bin/​env node console.log( Node ${process.version} ); console.log(JSON.stringify(process. env , null, 2 ));

python-script : #!/​usr/​bin/​env python3 import sys print(f " Python {sys.version}" )

bash-script : #!/​usr/​bin/​env bash set -euo pipefail echo " Running on $(uname -s)"

When to use which:

[script()] - Better cross-platform support, cleaner syntax

Shebang - Traditional Unix approach, works without set unstable

Modules & Imports

Import Pattern

Include recipes from another file:

import " ./​just/​settings.just" import " ./​just/​base.just" import ? " ./​local.just" # Optional (no error if missing)

Module Pattern

Load submodule (requires set unstable ):

mod foo # Loads foo.just or foo/​justfile mod bar " path/​to/​bar" # Custom path mod ? optional # Optional module

Call module recipes

just foo : : build

Devkit Import Pattern

For projects using @sablier/​devkit :

import " ./​node_modules/​@sablier/​devkit/​just/​base.just" import " ./​node_modules/​@sablier/​devkit/​just/​npm.just"

Section Organization

Standard section header format:

----------------------------------------------------------------------------

DEPENDENCIES

----------------------------------------------------------------------------

Common sections (in order):

DEPENDENCIES - Required tools with URLs

CONSTANTS - Glob patterns, environment vars

RECIPES / COMMANDS - Main entry points

CHECKS - Code quality recipes

UTILITIES / INTERNAL HELPERS - Private helpers

Default Recipe

Always define a default recipe:

Show available commands

default : @ just --list

Dependencies Declaration

Document required tools at the top:

----------------------------------------------------------------------------

DEPENDENCIES

----------------------------------------------------------------------------

Bun: https://bun.sh

bun := require ( " bun" )

Ni: https://github.com/antfu-collective/ni

na := require ( " na" ) ni := require ( " ni" ) nlx := require ( " nlx" )

Usage: invoke directly in recipes (not with interpolation)

build : bun next build

Note: require() validates the tool exists at recipe evaluation time. Use the variable name directly (e.g., bun ), not with interpolation ( {{ bun }} ).

Context7 Fallback

For Just features not covered in this skill (new attributes, advanced functions, edge cases), fetch the latest documentation:

Use context7 MCP with library ID /​websites/​just_systems-man to get up-to-date Just documentation.

Example topics to search:

modules import mod - Module system details

settings - All available settings

attributes - Recipe attributes

functions - Built-in functions

script recipes - Script block syntax

Additional Resources

Reference Files

For detailed patterns and comprehensive coverage, consult:

references/​JUST_FEATURES.md - Complete settings, modules, attributes, functions reference

references/​PATTERNS.md - Established conventions, section organization, helper patterns

Example Templates

Working justfile templates in examples/ :

devkit.just - Minimal template importing @sablier/​devkit

standalone.just - Full standalone template with all patterns

External Documentation

Official Manual : https://just.systems/man/en/

GitHub Repository : https://github.com/casey/just

Context7 Library ID : /​websites/​just_systems-man

Important Limitations

Just does not support flags. Recipe parameters are positional only:

WRONG: Flags don't work

build -- release : # This won ' t work !

CORRECT: Use positional parameters

build mode = " debug" : cargo build {{ if mode == " release" { " --release" } else { " " } }}

Usage: just build release

For complex flag-like behavior, use environment variables or positional parameters with defaults.

Tips

Use @ prefix to suppress command echo: @echo "quiet"

Use + for variadic parameters: test +args

Use * for optional variadic: build *flags

Quote glob patterns in variables: GLOBS := ""**/​*.json""

Use [no-cd] in monorepos to stay in current directory

Private recipes start with _ or use [private]

Always define aliases after recipe names for discoverability