Skip to content
>_devvkit
$devvkit learn --librarie act-&-just-guide

Act & Just Guide

[task-runner][ci][automation][cli]
Automation & CI/CD
Install
# Act:
brew install act
# or: curl https://raw.githubusercontent.com/nektos/act/master/install.sh | sudo bash

# Just:
brew install just
# or: cargo install just
# Windows: winget install --id=Casey.Just

Act runs your GitHub Actions workflows locally. Before pushing, run `act` to test that your CI pipeline works — no waiting for GitHub runners. It uses Docker containers to simulate the GitHub Actions environment, supports secrets via `.secrets` file, and matrix strategies.

Just is a command runner (like `make` but simpler). Define commands in a `justfile` with dependencies, arguments, and cross-platform compatibility. `just build`, `just test`, `just deploy` — each runs the shell commands you define. No Makefile weirdness.

Act: use `act -j build` to run a specific job, `act --list` to see all jobs, `act -W .github/workflows/deploy.yml` for non-default workflow files. Just: use `just --list` to see available recipes, `just --dry-run` to preview commands, `just variable=value recipe` to override parameters.

Act Basics

Act — run all jobs— Run full CI locally.
act                          # Default: push event
act pull_request              # Simulate PR event
act --job lint                # Run specific job only
act --list                    # List all jobs
act -W .github/workflows/test.yml  # Specific workflow file

Act Options

Act — with secrets— Pass secrets to workflow.
# .secrets file:
DOCKER_USERNAME=myuser
DOCKER_PASSWORD=mypass

act --secret-file .secrets

# Or inline:
act -s MY_SECRET=value

# Skip local checks for large secrets:
echo "DOCKER_PASSWORD" >> .actignore
Act — matrix strategy— Test multiple versions.
# Act runs matrix strategies by default.
# To limit:
act --matrix node-version:18          # Only node 18
act --matrix os:ubuntu-latest    # Only Ubuntu

# With custom GitHub token (higher rate limits):
act -G token  # or GITHUB_TOKEN env var
Act — use Docker image— Custom runner image.
act -P ubuntu-latest=catthehacker/ubuntu:full-latest
act -P ubuntu-latest=node:20-bookworm-slim

# List available images:
act --list-images

# Clean cached images:
docker system prune -a  # Act caches images locally

Just Basics

Just — hello world— Simple justfile.
# justfile
build:
    npm run build

test:
    npm test

lint:
    npx eslint src/

deploy: build test
    echo "Ready to deploy"

# Run:
# just build
# just test
# just deploy  # runs build → test → deploy
Just — dry run— Preview commands.
just --dry-run deploy           # Show commands without running
just --highlight                # Colorize justfile
just --list                     # List all recipes
just --summary                  # List with descriptions
just --evaluate                 # Print evaluated variables
just --init                     # Create minimal justfile

Justfiles

Just — with arguments— Parameterized recipes.
# justfile
node_image := "node:20"
port := "3000"

build arch:
    docker build --platform linux/{{arch}} -t myapp .

serve name="default":
    docker run -p {{port}}:3000 --name {{name}} myapp

clean *targets:
    for target in {{targets}}; do
        rm -rf ./dist/$target
    done

# Run:
# just build amd64
# just serve my-container
# just clean app1 app2 app3
Just — cross-platform— Windows/macOS/Linux.
# justfile
alias b := build

[no-cd]
build:
    npm run build

[no-exit-message]
clean:
    rm -rf dist/

[windows]
clean:
    if exist dist rmdir /s /q dist

# Commands run with cmd.exe on Windows, sh on macOS/Linux
# Just handles OS-specific recipes
Just — dotenv— Load environment files.
# justfile
dotenv: .env.local

set positional-arguments := true

serve:
    echo $DATABASE_URL
    npm run dev

# .env.local:
# DATABASE_URL=postgres://localhost:5432/dev

# Check env:
just --dotenv-filename .env.production serve