Github Actions

GitHub Actions

Activate when creating, modifying, troubleshooting, or optimizing GitHub Actions components. This skill covers action development, marketplace integration, and best practices.

When to Use This Skill

Activate when:

• Creating custom GitHub Actions (JavaScript, Docker, or composite)
• Publishing actions to GitHub Marketplace
• Configuring action metadata and inputs/outputs
• Implementing action security and permissions
• Troubleshooting action execution
• Selecting or evaluating marketplace actions
• Optimizing action performance and reliability

Action Types

JavaScript Actions

Execute directly on runners with fast startup and cross-platform compatibility.

Structure:

my-action/
├── action.yml        # Metadata and interface
├── index.js          # Entry point
├── package.json      # Dependencies
└── node_modules/     # Bundled dependencies

Key Requirements:

• Use @actions/core for inputs/outputs
• Use @actions/github for GitHub API access
• Bundle all dependencies (use @vercel/ncc)
• Support Node.js LTS versions

Example action.yml:

name: 'My JavaScript Action'
description: 'Performs custom task'
inputs:
  token:
    description: 'GitHub token'
    required: true
  config:
    description: 'Configuration file path'
    required: false
    default: 'config.yml'
outputs:
  result:
    description: 'Action result'
runs:
  using: 'node20'
  main: 'dist/index.js'

Docker Container Actions

Provide consistent execution environment with all dependencies packaged.

Structure:

my-action/
├── action.yml
├── Dockerfile
├── entrypoint.sh
└── src/

Key Requirements:

• Use lightweight base images (Alpine when possible)
• Set proper file permissions
• Handle signals gracefully
• Output to STDOUT/STDERR correctly

Example Dockerfile:

FROM alpine:3.18

RUN apk add --no-cache bash curl jq

COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh

ENTRYPOINT ["/entrypoint.sh"]

Composite Actions

Combine multiple steps and actions into reusable units.

Structure:

name: 'Setup Environment'
description: 'Configure development environment'
inputs:
  node-version:
    description: 'Node.js version'
    required: false
    default: '20'
runs:
  using: 'composite'
  steps:
    - uses: actions/setup-node@v4
      with:
        node-version: ${{ inputs.node-version }}
    - run: npm ci
      shell: bash
    - run: npm run build
      shell: bash

Action Metadata (action.yml)

Required Fields

name: 'Action Name'           # Marketplace display name
description: 'What it does'   # Clear, concise purpose
runs:                         # Execution configuration
  using: 'node20'            # or 'docker' or 'composite'

Optional Fields

author: 'Your Name'
branding:                    # Marketplace icon/color
  icon: 'activity'
  color: 'blue'
inputs:                      # Define all inputs
  input-name:
    description: 'Purpose'
    required: true
    default: 'value'
outputs:                     # Define all outputs
  output-name:
    description: 'What it contains'

Inputs and Outputs

Reading Inputs

JavaScript:

const core = require('@actions/core');
const token = core.getInput('token', { required: true });
const config = core.getInput('config') || 'default.yml';

Shell:

TOKEN="${{ inputs.token }}"
CONFIG="${{ inputs.config }}"

Setting Outputs

JavaScript:

core.setOutput('result', 'success');
core.setOutput('artifact-url', artifactUrl);

Shell:

echo "result=success" >> $GITHUB_OUTPUT
echo "artifact-url=$ARTIFACT_URL" >> $GITHUB_OUTPUT

GitHub Actions Toolkit

Essential npm packages for JavaScript actions:

@actions/core

const core = require('@actions/core');

// Inputs/Outputs
const input = core.getInput('name');
core.setOutput('name', value);

// Logging
core.info('Information message');
core.warning('Warning message');
core.error('Error message');
core.debug('Debug message');

// Grouping
core.startGroup('Group name');
// ... operations
core.endGroup();

// Failure
core.setFailed('Action failed: reason');

// Secrets
core.setSecret('sensitive-value');  // Masks in logs

// Environment
core.exportVariable('VAR_NAME', 'value');

@actions/github

const github = require('@actions/github');

// Context
const context = github.context;
console.log(context.repo);        // { owner, repo }
console.log(context.sha);         // Commit SHA
console.log(context.ref);         // Branch/tag ref
console.log(context.actor);       // Triggering user
console.log(context.payload);     // Webhook payload

// Octokit client
const token = core.getInput('token');
const octokit = github.getOctokit(token);

// API operations
const { data: issues } = await octokit.rest.issues.listForRepo({
  owner: context.repo.owner,
  repo: context.repo.repo,
  state: 'open'
});

@actions/exec

const exec = require('@actions/exec');

// Execute commands
await exec.exec('npm', ['install']);

// Capture output
let output = '';
await exec.exec('git', ['log', '--oneline'], {
  listeners: {
    stdout: (data) => { output += data.toString(); }
  }
});

Security Best Practices

Input Validation

Always validate and sanitize inputs:

const core = require('@actions/core');

function validateInput(input) {
  // Check for command injection
  if (/[;&|`$()]/.test(input)) {
    throw new Error('Invalid characters in input');
  }
  return input;
}

const userInput = core.getInput('user-input');
const safeInput = validateInput(userInput);

Token Permissions

Request minimal required permissions:

permissions:
  contents: read           # Read repository
  pull-requests: write     # Comment on PRs
  issues: write           # Create issues

Secret Handling

// Mask secrets in logs
core.setSecret(sensitiveValue);

// Never log tokens
core.debug(`Token: ${token}`);  // ❌ WRONG
core.debug('Token received');   // ✅ CORRECT

// Secure token usage
const octokit = github.getOctokit(token);
// Token automatically included in requests

Dependency Security

# Audit dependencies
npm audit

# Use specific versions
npm install @actions/core@1.10.0

# Bundle dependencies
npm install -g @vercel/ncc
ncc build index.js -o dist

Marketplace Publishing

Prerequisites

• Public repository
• action.yml in repository root
• README.md with usage examples
• LICENSE file
• Repository topics (optional)

Publishing Process

1. Create release with semantic version tag:

git tag -a v1.0.0 -m "Release v1.0.0"
git push origin v1.0.0

2. Create GitHub Release from tag
3. Check "Publish this Action to GitHub Marketplace"
4. Select primary category
5. Verify branding icon/color

Version Management

Use semantic versioning with major version tags:

# Release v1.2.3
git tag -a v1.2.3 -m "Release v1.2.3"
git tag -fa v1 -m "Update v1 to v1.2.3"
git push origin v1.2.3 v1 --force

Users reference by major version:

- uses: owner/action@v1  # Tracks latest v1.x.x

Testing Actions Locally

Use act for local testing (see act skill):

# Test action in current directory
act -j test

# Test with specific event
act push

# Test with secrets
act -s GITHUB_TOKEN=ghp_xxx

Common Patterns

Matrix Testing Action

# action.yml
name: 'Matrix Test Runner'
description: 'Run tests across multiple configurations'
inputs:
  matrix-config:
    description: 'JSON matrix configuration'
    required: true
runs:
  using: 'composite'
  steps:
    - run: |
        echo "Testing with config: ${{ inputs.matrix-config }}"
        # Parse and execute tests
      shell: bash

Cache Management Action

const core = require('@actions/core');
const cache = require('@actions/cache');

async function run() {
  const paths = [
    'node_modules',
    '.npm'
  ];

  const key = `deps-${process.platform}-${hashFiles('package-lock.json')}`;

  // Restore cache
  const cacheKey = await cache.restoreCache(paths, key);

  if (!cacheKey) {
    core.info('Cache miss, installing dependencies');
    await exec.exec('npm', ['ci']);
    await cache.saveCache(paths, key);
  } else {
    core.info(`Cache hit: ${cacheKey}`);
  }
}

Artifact Upload Action

const artifact = require('@actions/artifact');

async function uploadArtifact() {
  const artifactClient = artifact.create();
  const files = [
    'dist/bundle.js',
    'dist/styles.css'
  ];

  const rootDirectory = 'dist';
  const options = {
    continueOnError: false
  };

  const uploadResponse = await artifactClient.uploadArtifact(
    'build-artifacts',
    files,
    rootDirectory,
    options
  );

  core.setOutput('artifact-id', uploadResponse.artifactId);
}

Troubleshooting

Action Not Found

• Verify repository is public or accessible
• Check action.yml exists in repository root
• Confirm version tag exists

Permission Denied

# Add required permissions to workflow
permissions:
  contents: write
  pull-requests: write

Node Modules Missing

• Bundle dependencies with ncc
• Check dist/ folder is committed
• Verify node_modules excluded from .gitignore for dist/

Docker Action Fails

• Check Dockerfile syntax
• Verify entrypoint has execute permissions
• Test container locally: docker build -t test . && docker run test

Anti-Fabrication Requirements

• Execute Read or Glob tools to verify action files exist before claiming structure
• Use Bash to test commands before documenting syntax
• Validate action.yml schema against actual files using tool analysis
• Execute actual API calls with @actions/github before documenting responses
• Test permission configurations in real workflows before recommending settings
• Never claim action capabilities without reading actual implementation code
• Report actual npm audit results when discussing security, not fabricated vulnerability counts