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 [arg("p", long, ...)] Configure parameter as --flag option (v1.46) [arg("p", pattern="…")] Constrain parameter to match regex pattern [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 Recipe Argument Flags (v1.46.0+) The [arg()] attribute configures parameters as CLI-style options:
Long option (--target)
[arg("target", long)] build target: cargo build --target {{ target }}
Short option (-v)
[arg("verbose", short="v")] run verbose="false": echo "Verbose: {{ verbose }}"
Combined long + short
[arg("output", long, short="o")] compile output: gcc main.c -o {{ output }}
Flag without value (presence sets to "true")
[arg("release", long, value="true")] build release="false": cargo build {{ if release == "true" { "--release" } else { "" } }}
Help string (shown in just --usage)
[arg("target", long, help="Build target architecture")] build target: cargo build --target {{ target }} Usage examples: just build --target x86_64 just build --target = x86_64 just compile -o main just build --release just --usage build
Show recipe argument help
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 , MAGENTA 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/settings.md
- Settings configuration and module system
references/recipes.md
- Recipe attributes, parameters, dependencies, and prefixes
references/syntax.md
- Constants, functions, variables, and CLI options
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
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