act - Local GitHub Actions Testing

Activate when testing GitHub Actions workflows locally, debugging workflow issues, or developing actions without committing to remote repositories. This skill covers act installation, configuration, and usage patterns.

When to Use This Skill

Activate when:

• Testing workflow changes before committing
• Debugging workflow failures locally
• Developing new workflows iteratively
• Validating workflow syntax and logic
• Testing actions with different events
• Running workflows without GitHub runners
• Troubleshooting act-specific issues

Installation

Using mise (Recommended for this project)

The act tool is configured in the github plugin's mise.toml:

# Install act via mise
mise install act

# Verify installation
act --version

Alternative Installation Methods

macOS (Homebrew):

brew install act

Linux (via script):

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

From source:

git clone https://github.com/nektos/act.git
cd act
make install

Windows (Chocolatey):

choco install act-cli

How act Works

act reads workflow files from

.github/workflows/

and:

1. Determines which actions and jobs to execute
2. Pulls or builds required Docker images
3. Creates containers matching GitHub's runner environment
4. Executes steps in isolated containers
5. Provides output matching GitHub Actions format

Key Concept: act uses Docker to simulate GitHub's runner environment locally.

Prerequisites

• Docker: act requires Docker to run workflows
• Workflow files: Valid

  .github/workflows/*.yml

  files in repository

Verify Docker is running:

docker ps

Basic Usage

List Available Workflows

# List all workflows
act -l

# Output:
# Stage  Job ID  Job name  Workflow name  Workflow file  Events
# 0      build   build     CI             ci.yml         push,pull_request
# 0      test    test      CI             ci.yml         push,pull_request

Run Default Event (push)

# Run all jobs triggered by push event
act

# Run specific job
act -j build

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

Run Specific Events

# Pull request event
act pull_request

# Manual workflow dispatch
act workflow_dispatch

# Push to specific branch
act push -e .github/workflows/push-event.json

# Schedule event
act schedule

Dry Run

# Show what would run without executing
act -n

# Show with full details
act -n -v

Event Payloads

Custom Event Data

Create event JSON file:

{
  "pull_request": {
    "number": 123,
    "head": {
      "ref": "feature-branch"
    },
    "base": {
      "ref": "main"
    }
  }
}

Use with act:

act pull_request -e event.json

workflow_dispatch Inputs

{
  "inputs": {
    "environment": "staging",
    "debug": true
  }
}

act workflow_dispatch -e inputs.json

Secrets Management

Via Command Line

# Single secret
act -s GITHUB_TOKEN=ghp_xxxxx

# Multiple secrets
act -s API_KEY=key123 -s DB_PASSWORD=pass456

Via .secrets File

Create

.secrets

file (add to .gitignore):

GITHUB_TOKEN=ghp_xxxxx
API_KEY=key123
DB_PASSWORD=pass456

Run with secrets file:

act --secret-file .secrets

Environment Variables

# Use existing env var
act -s GITHUB_TOKEN

# Set from command
export MY_SECRET=value
act -s MY_SECRET

Configuration

.actrc File

Create

.actrc

in repository root or home directory:

# Use specific platform
-P ubuntu-latest=catthehacker/ubuntu:act-latest

# Default secrets file
--secret-file .secrets

# Default environment
--env-file .env

# Container architecture
--container-architecture linux/amd64

# Verbose output
-v

Custom Runner Images

# Use custom image for platform
act -P ubuntu-latest=my-custom-image:latest

# Use medium size images (recommended)
act -P ubuntu-latest=catthehacker/ubuntu:act-latest

# Use micro images (faster, less compatible)
act -P ubuntu-latest=node:16-buster-slim

Recommended Images

act supports different image sizes:

Medium images (recommended):

• Better compatibility with GitHub Actions
• More pre-installed tools
• Slower startup but fewer failures

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

Micro images:

• Faster startup
• Minimal pre-installed tools
• May require additional setup

Environment Variables

Via .env File

Create

.env

file:

NODE_ENV=test
API_URL=http://localhost:3000
LOG_LEVEL=debug

Use with act:

act --env-file .env

Via Command Line

act --env NODE_ENV=test --env API_URL=http://localhost:3000

Advanced Usage

Bind Workspace

Mount local directory into container:

act --bind

Reuse Containers

Keep containers between runs for faster execution:

act --reuse

Specific Platforms

# Run on specific platform
act -P ubuntu-latest=ubuntu:latest

# Multiple platforms
act -P ubuntu-latest=ubuntu:latest \
    -P windows-latest=windows:latest

Container Architecture

# Specify architecture (useful for M1/M2 Macs)
act --container-architecture linux/amd64

Network Configuration

# Use host network
act --container-daemon-socket -

# Custom network
act --network my-network

Artifact Server

# Enable artifact server on specific port
act --artifact-server-path /tmp/artifacts \
    --artifact-server-port 34567

Debugging

Verbose Output

# Verbose logging
act -v

# Very verbose (debug level)
act -vv

Watch Mode

# Watch for file changes and re-run
act --watch

Interactive Shell

# Drop into shell on failure
act --shell bash

Container Inspection

# List act containers
docker ps -a | grep act

# Inspect specific container
docker inspect <container-id>

# View logs
docker logs <container-id>

Limitations and Differences

Not Supported by act

• Some GitHub-hosted runner features
• GitHub Apps and installations
• OIDC token generation
• Some GitHub API interactions
• Certain cache implementations
• Job summaries and annotations (limited)

Workarounds

Missing tools:

steps:
  - name: Install missing tool
    run: |
      if ! command -v tool &> /dev/null; then
        apt-get update && apt-get install -y tool
      fi

GitHub API calls:

# Use GITHUB_TOKEN from secrets
- env:
    GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
  run: gh api repos/${{ github.repository }}/issues

Common Patterns

Testing Pull Request Workflow

# Create PR event payload
cat > pr-event.json << EOF
{
  "pull_request": {
    "number": 1,
    "head": { "ref": "feature" },
    "base": { "ref": "main" }
  }
}
EOF

# Run PR workflow
act pull_request -e pr-event.json -j test

CI/CD Pipeline Testing

# Test entire CI pipeline
act push

# Test specific stages
act push -j build
act push -j test
act push -j deploy --secret-file .secrets

Matrix Testing

# Run matrix strategy locally
act -j test

# Test specific matrix combination (modify workflow temporarily)
act -j test --matrix node-version:20

Workflow Development Cycle

# 1. List jobs
act -l

# 2. Dry run
act -n -j build

# 3. Run with verbose output
act -v -j build

# 4. Iterate and test
act --reuse -j build

Troubleshooting

Docker Issues

Error: Cannot connect to Docker daemon

# Start Docker
# macOS: Start Docker Desktop
# Linux:
sudo systemctl start docker

Error: Permission denied

# Add user to docker group (Linux)
sudo usermod -aG docker $USER
newgrp docker

Image Pull Issues

Error: Failed to pull image

# Use specific image version
act -P ubuntu-latest=ubuntu:22.04

# Or use act's recommended images
act -P ubuntu-latest=catthehacker/ubuntu:act-latest

Workflow Not Found

Error: No workflows found

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

# Check workflow syntax
act -n -v

Secret Issues

Error: Secret not found

# List required secrets from workflow
grep -r "secrets\." .github/workflows/

# Provide via command line
act -s SECRET_NAME=value

# Or use secrets file
act --secret-file .secrets

Action Failures

Error: Action not found or fails

# Ensure action versions are compatible
# Some actions may not work locally

# Use alternative actions if needed
# Or skip problematic steps locally:
- name: Problematic step
  if: github.event_name != 'act'  # Skip in act
  uses: some/action@v1

Platform Differences

Error: Command not found

# Use medium-sized images with more tools
act -P ubuntu-latest=catthehacker/ubuntu:act-latest

# Or install tools in workflow
- run: apt-get update && apt-get install -y <tool>

Best Practices

.actrc Configuration

Create

.actrc

in repository:

-P ubuntu-latest=catthehacker/ubuntu:act-latest
--secret-file .secrets
--container-architecture linux/amd64
--artifact-server-path /tmp/artifacts

.gitignore Entries

# act secrets and config
.secrets
.env

# act artifacts
/tmp/artifacts/

Conditional Logic for Local Testing

steps:
  # Skip in local testing
  - name: Deploy
    if: github.event_name != 'act'
    run: ./deploy.sh

  # Run only in local testing
  - name: Local setup
    if: github.event_name == 'act'
    run: ./local-setup.sh

Fast Feedback Loop

# Use reuse flag for faster iterations
act --reuse -j test

# Run specific job being developed
act -j my-new-job -v

# Watch mode for continuous testing
act --watch -j test

Integration with Development Workflow

Pre-commit Testing

# Test before committing
act -j test && git commit -m "message"

# Git hook (.git/hooks/pre-commit)
#!/bin/bash
act -j test --quiet

Quick Validation

# Validate workflow syntax
act -n

# Test specific changes
act -j affected-job

CI Parity

# Use same images as CI
act -P ubuntu-latest=ubuntu:22.04

# Use same secrets structure
act --secret-file .secrets

Scripts and Automation

Installation Script

The plugin includes an installation script at

scripts/install-act.sh

:

#!/usr/bin/env bash
# Install act via mise or fallback methods

if command -v mise &> /dev/null; then
  echo "Installing act via mise..."
  mise install act
elif [[ "$OSTYPE" == "darwin"* ]] && command -v brew &> /dev/null; then
  echo "Installing act via Homebrew..."
  brew install act
elif [[ "$OSTYPE" == "linux-gnu"* ]]; then
  echo "Installing act via install script..."
  curl -s https://raw.githubusercontent.com/nektos/act/master/install.sh | sudo bash
else
  echo "Please install act manually: https://github.com/nektos/act"
  exit 1
fi

act --version

Run with:

chmod +x scripts/install-act.sh
./scripts/install-act.sh

Anti-Fabrication Requirements

• Execute

  act --version

  before documenting version numbers
• Use

  act -l

  to verify actual workflows before claiming their presence
• Execute

  docker ps

  to confirm Docker is running before troubleshooting
• Run

  act -n

  to validate workflow syntax before claiming correctness
• Execute actual

  act

  commands to verify behavior before documenting output format
• Use

  docker images

  to verify available images before recommending specific versions
• Never claim success rates or performance metrics without actual measurement
• Execute

  act -v

  to observe actual error messages before documenting troubleshooting steps
• Use Read tool to verify workflow files exist before testing them with act
• Run actual event payloads through act before claiming they work correctly