work-with-justfiles

The goal is a single source of truth for "how do I do X in this repo" that anyone can read and understand.

<quick_start> <core_rule> Justfiles always run from the repo root. Never cd in recipes. Use absolute paths or paths relative to the justfile location. </core_rule>

<basic_structure>

# Group: Development
dev:
    npm run dev

# Group: Testing
test:
    npm test

test-watch:
    npm test -- --watch

</basic_structure> </quick_start>

<essential_principles> Always run from root, never cd

Justfiles execute from the repository root. This is a feature, not a limitation:

• Predictable behavior regardless of where you invoke just
• Paths in recipes are always relative to repo root
• No confusion about "where am I running this from"

# Good - explicit path from root
build:
    cd packages/app && npm run build

# Bad - assumes current directory
build:
    npm run build

If a command needs to run in a subdirectory, use cd dir && prefix explicitly.

The justfile should be the single source of truth for repo commands. If someone asks "how do I run tests?" or "how do I deploy?", the answer is in the justfile.

# Instead of remembering: npm run test:unit -- --coverage --reporter=html
test-coverage:
    npm run test:unit -- --coverage --reporter=html

# Instead of remembering: docker compose -f docker-compose.dev.yml up -d
dev-services:
    docker compose -f docker-compose.dev.yml up -d

Benefits:

• No tribal knowledge ("oh you need to pass --reporter=html")
• Commands are documented by their existence
• Easy to discover: just --list

Use comments to create visual groupings. Let the groups emerge from your actual commands:

# ─────────────────────────────────────────────────────────────
# Development
# ─────────────────────────────────────────────────────────────

dev:
    npm run dev

# ─────────────────────────────────────────────────────────────
# Testing
# ─────────────────────────────────────────────────────────────

test:
    npm test

test-watch:
    npm test -- --watch

Common groupings (adapt to your project):

• Setup / Installation
• Development
• Testing
• Building
• Deployment
• Database / Migrations
• Utilities / Helpers

Justfiles replace scattered shell commands and npm scripts for common operations. They don't replace:

• Build tool configuration (webpack, vite, etc.)
• CI/CD pipeline definitions
• Complex scripting (use actual scripts in scripts/)

Rule of thumb: If a recipe is longer than 5-10 lines, extract it to a script file and call that from the justfile:

# Good - justfile calls the script
deploy:
    ./scripts/deploy.sh

# Avoid - complex logic inline
deploy:
    if [ "$ENV" = "prod" ]; then
        # ... 20 lines of logic
    fi

Use recipe names that describe the workflow, not the tool:

# Good - describes what you're doing
setup:
    npm install
    cp .env.example .env
    just db-migrate

# Less good - just wraps the tool
npm-install:
    npm install

Chain related commands with dependencies:

# Running `just deploy` runs lint, test, build first
deploy: lint test build
    ./scripts/deploy.sh

The first recipe (or one named default) runs when you type just just:

# Show available commands by default
default:
    @just --list

# Or start development by default
default:
    just dev

# Positional argument
test file:
    npm test {{file}}

# With default value
build env="dev":
    npm run build -- --env={{env}}

# Variadic arguments
run *args:
    npm run {{args}}

# From .env file
set dotenv-load

# Inline variable
db_name := "myapp_dev"

# Recipe-local export
migrate:
    export DATABASE_URL=$DATABASE_URL && npm run migrate

[confirm("Are you sure you want to reset the database?")]
db-reset:
    dropdb myapp && createdb myapp && just db-migrate

Prefix with _ to hide from just --list:

# Public - shows in list
build: _check-deps
    npm run build

# Private - hidden helper
_check-deps:
    @command -v node >/dev/null || (echo "Node required" && exit 1)

# Deploy to production (requires VPN connection)
[doc("Deploy the application to production environment")]
deploy-prod:
    ./scripts/deploy.sh prod

<anti_patterns> Avoid changing directory implicitly

# Bad - unclear where this runs
build:
    cd src
    npm run build

# Good - explicit and stays in root
build:
    cd src && npm run build

If npm run dev is obvious and memorable, you don't need just dev unless it adds value (like running setup first).

Add justfile recipes when:

• The command has flags that are hard to remember
• Multiple commands need to run together
• The command needs environment setup

Before: Developers need to know npm, docker-compose, aws, terraform, kubectl...

After: just --list shows everything, actual tools are implementation details.

# These hide complexity behind simple names
deploy:
    terraform apply -auto-approve

db-shell:
    kubectl exec -it postgres-0 -- psql

<success_criteria> A well-organized justfile:

• Runs all commands from repo root (no implicit cd)
• Has logical groupings with clear visual separation
• Captures common commands as aliases (single source of truth)
• Uses descriptive recipe names (workflow-focused, not tool-focused)
• Keeps recipes short (complex logic in scripts/)
• Has a sensible default recipe
• Is discoverable via just --list </success_criteria>