Act - Local Workflow Testing

Use this skill when testing GitHub Actions workflows locally with act. This covers act CLI commands, Docker setup, debugging, and best practices for fast local iteration on CI/CD workflows.

Installation

macOS

brew install act

Linux

curl -s https://raw.githubusercontent.com/nektos/act/master/install.sh | sudo bash

Windows

choco install act-cli
# or
scoop install act

From Source

go install github.com/nektos/act@latest

Basic Usage

Run All Workflows

# Run workflows triggered by push event
act

# Equivalent to
act push

Run Specific Events

# Pull request event
act pull_request

# Workflow dispatch
act workflow_dispatch

# Custom event
act repository_dispatch -e event.json

Run Specific Workflows

# Run specific workflow file
act -W .github/workflows/ci.yml

# Run specific job
act -j build

# Run specific workflow and job
act -W .github/workflows/deploy.yml -j production

List Available Workflows

# List all workflows and jobs
act -l

# List for specific event
act pull_request -l

Validation and Dry Runs

Dry Run

# Validate without executing
act --dryrun

# Show what would run
act -n

# Validate specific workflow
act --dryrun -W .github/workflows/ci.yml

Graph Visualization

# Show workflow graph
act -g

# Show graph for specific event
act pull_request -g

Docker Configuration

Default Runners

Act uses Docker images to simulate GitHub's runners:

# Use default images (micro - minimal)
act

# Use medium images (more tools)
act -P ubuntu-latest=catthehacker/ubuntu:act-latest

# Use large images (most compatible)
act -P ubuntu-latest=catthehacker/ubuntu:full-latest

Custom Platform Images

Create .actrc file in project root:

-P ubuntu-latest=catthehacker/ubuntu:act-latest
-P ubuntu-22.04=catthehacker/ubuntu:act-22.04
-P ubuntu-20.04=catthehacker/ubuntu:act-20.04

Or use command line:

act -P ubuntu-latest=node:18 \
    -P ubuntu-22.04=catthehacker/ubuntu:act-22.04

Reusing Docker Containers

# Reuse containers between runs (faster)
act --reuse

# Clean up after run
act --rm

Secrets Management

Using .secrets File

Create .secrets in project root:

GITHUB_TOKEN=ghp_your_token_here
NPM_TOKEN=npm_your_token_here
AWS_ACCESS_KEY_ID=your_key
AWS_SECRET_ACCESS_KEY=your_secret

Add to .gitignore:

.secrets

Run with secrets:

act --secret-file .secrets

Inline Secrets

# Single secret
act -s GITHUB_TOKEN=ghp_token

# Multiple secrets
act -s GITHUB_TOKEN=ghp_token \
    -s NPM_TOKEN=npm_token

Environment-Specific Secrets

# Development secrets
act --secret-file .secrets.dev

# Production secrets
act --secret-file .secrets.prod

Environment Variables

Setting Variables

# Single variable
act --env NODE_ENV=development

# Multiple variables
act --env NODE_ENV=development \
    --env DEBUG=true

Using .env File

Create .env file:

NODE_ENV=development
DEBUG=true
LOG_LEVEL=debug

Run with env file:

act --env-file .env

GitHub Context Variables

Act automatically sets these:

GITHUB_ACTOR=nektos/act
GITHUB_REPOSITORY=owner/repo
GITHUB_EVENT_NAME=push
GITHUB_SHA=abc123...
GITHUB_REF=refs/heads/main
ACT=true

Debugging

Verbose Output

# Verbose mode
act -v

# Very verbose (debug)
act -vv

Step-by-Step Execution

# Interactive mode - pause before each step
act --watch

Inspect Containers

# Keep container running after workflow
act --reuse

# Then in another terminal
docker ps
docker exec -it <container-id> /bin/bash

Bind Mount Local Files

# Mount current directory
act --bind

# Mount specific directory
act -b /host/path:/container/path

Common Workflows

Test Before Push

# Validate workflow syntax
act --dryrun

# Run tests
act -j test

# Run full CI
act

Iterative Development

# Edit workflow
vim .github/workflows/ci.yml

# Test immediately
act --reuse -j build

# Iterate quickly
act --reuse -j build

Matrix Testing

# Run specific matrix combination
act --matrix os:ubuntu-latest --matrix node:20

# Run all combinations
act

Troubleshooting

Docker Issues

# Check Docker is running
docker ps

# Pull required images manually
docker pull catthehacker/ubuntu:act-latest

# Clean up Docker resources
docker system prune -a

Permission Issues

# Run with sudo (Linux)
sudo act

# Fix Docker permissions (Linux)
sudo usermod -aG docker $USER
newgrp docker

Missing Tools

# Use fuller image
act -P ubuntu-latest=catthehacker/ubuntu:full-latest

# Or install in workflow
- run: |
    apt-get update
    apt-get install -y some-tool

Workflow Not Found

# Check workflow files exist
ls -la .github/workflows/

# Validate YAML syntax
yamllint .github/workflows/*.yml

# List detected workflows
act -l

Action Compatibility

Some actions don't work with act:

# Skip action in act
- name: GitHub-only action
  if: ${{ !env.ACT }}
  uses: github/some-action@v1

# Use alternative in act
- name: Local alternative
  if: env.ACT == 'true'
  run: echo "Running local version"

Best Practices

DO

✅ Use act --dryrun before running full workflows
✅ Create .actrc for consistent configuration
✅ Use .secrets file and add it to .gitignore
✅ Use --reuse for faster iteration
✅ Test workflows locally before pushing
✅ Use appropriate image sizes for your needs
✅ Document act usage in README

DON'T

❌ Commit .secrets or .env files
❌ Use latest Docker tags in production
❌ Skip validation with --dryrun
❌ Run act without understanding what it will do
❌ Ignore Docker disk space usage
❌ Assume all actions work perfectly with act

Configuration Files

.actrc

# Platform mappings
-P ubuntu-latest=catthehacker/ubuntu:act-latest

# Default options
--reuse
--secret-file .secrets
--env-file .env

# Container options
--container-architecture linux/amd64

.github/workflows/.actrc

Project-specific overrides in workflows directory.

CI/CD Integration

Pre-Push Hook

.git/hooks/pre-push:

#!/bin/bash
echo "Validating workflows..."
act --dryrun
if [ $? -ne 0 ]; then
  echo "Workflow validation failed"
  exit 1
fi

Make Target

.PHONY: test-workflows
test-workflows:
 act --dryrun
 act -j test

.PHONY: ci-local
ci-local:
 act --reuse

Performance Tips

Faster Iteration

# Use reuse flag
act --reuse

# Skip checkout if not needed
act --reuse -j test --no-recurse

# Use smaller images for simple tests
act -P ubuntu-latest=node:20-alpine

Caching

Act respects GitHub Actions caching:

- uses: actions/cache@v4
  with:
    path: ~/.npm
    key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

Cache location on host: ~/.cache/act/

Related Skills

• act-workflow-syntax: Creating and structuring workflow files
• act-docker-setup: Configuring Docker for act
• act-advanced-features: Advanced act usage patterns