GitHub Actions Validator

Overview

Validate and test GitHub Actions workflows, custom actions, and public actions using industry-standard tools (actionlint and act). This skill provides comprehensive validation including syntax checking, static analysis, local workflow execution testing, and action verification with version-aware documentation lookup.

When to Use This Skill

Use this skill when:

• Validating workflow files: Checking .github/workflows/*.yml for syntax errors and best practices
• Testing workflows locally: Running workflows with act before pushing to GitHub
• Debugging workflow failures: Identifying issues in workflow configuration
• Validating custom actions: Checking composite, Docker, or JavaScript actions
• Verifying public actions: Validating usage of actions from GitHub Marketplace
• Pre-commit validation: Ensuring workflows are valid before committing

CRITICAL: Assistant Workflow (MUST FOLLOW)

Every validation MUST follow these steps. Skipping any step is non-compliant.

Step 1: Run Validation Script

cd .claude/skills/github-actions-validator
bash scripts/validate_workflow.sh <workflow-file-or-directory>

Step 2: For EACH Error - Consult Reference File

When actionlint or act reports ANY error, you MUST:

1. Read the appropriate reference file (see mapping below)
2. Find the matching error pattern
3. Extract the fix/solution

Step 3: Quote the Fix to User

For each error, provide:

1. Error message (from script output)
2. Explanation (from reference file)
3. Fix code (quoted from reference file)
4. Corrected code (applied to user's workflow)

Step 4: Verify Public Actions (if present)

For any public actions (uses: owner/action@version):

1. First check references/action_versions.md for known actions and versions
2. Use web search for unknown actions: "[action-name] [version] github action documentation"
3. Verify required inputs match
4. Check for deprecation warnings

Step 5: Provide Complete Summary

After all errors are addressed:

• List all fixes applied
• Note any warnings
• Recommend best practices from references/

Error Type to Reference File Mapping

Example: Complete Error Handling Workflow

User's workflow has this error:

runs-on: ubuntu-lastest

Step 1 - Script output:

label "ubuntu-lastest" is unknown

Step 2 - Read references/runners.md or references/common_errors.md: Find the "Invalid Runner Label" section.

Step 3 - Quote the fix to user:

Error: label "ubuntu-lastest" is unknown

Cause: Typo in runner label (from references/common_errors.md):

# Bad
runs-on: ubuntu-lastest  # Typo

Fix (from references/common_errors.md):

# Good
runs-on: ubuntu-latest

Valid runner labels (from references/runners.md):

• ubuntu-latest, ubuntu-24.04, ubuntu-22.04
• windows-latest, windows-2025, windows-2022
• macos-latest, macos-15, macos-14

Step 4 - Provide corrected code:

runs-on: ubuntu-latest

Quick Start

Initial Setup

cd .claude/skills/github-actions-validator
bash scripts/install_tools.sh

This installs act (local workflow execution) and actionlint (static analysis) to scripts/.tools/.

Basic Validation

# Validate a single workflow
bash scripts/validate_workflow.sh .github/workflows/ci.yml

# Validate all workflows
bash scripts/validate_workflow.sh .github/workflows/

# Lint-only (fastest)
bash scripts/validate_workflow.sh --lint-only .github/workflows/ci.yml

# Test-only with act (requires Docker)
bash scripts/validate_workflow.sh --test-only .github/workflows/

Core Validation Workflow

1. Static Analysis with actionlint

Start with static analysis to catch syntax errors and common issues:

bash scripts/validate_workflow.sh --lint-only .github/workflows/ci.yml

What actionlint checks: YAML syntax, schema compliance, expression syntax, runner labels, action inputs/outputs, job dependencies, CRON syntax, glob patterns, shell scripts, security vulnerabilities.

2. Local Testing with act

After passing static analysis, test workflow execution:

bash scripts/validate_workflow.sh --test-only .github/workflows/

Note: act has limitations - see references/act_usage.md.

3. Full Validation

bash scripts/validate_workflow.sh .github/workflows/ci.yml

Validating Resource Types

Workflows

# Single workflow
bash scripts/validate_workflow.sh .github/workflows/ci.yml

# All workflows
bash scripts/validate_workflow.sh .github/workflows/

Key validation points: triggers, job configurations, runner labels, environment variables, secrets, conditionals, matrix strategies.

Custom Local Actions

Create a test workflow that uses the custom action, then validate:

bash scripts/validate_workflow.sh .github/workflows/test-custom-action.yml

Public Actions

When workflows use public actions (e.g., actions/checkout@v6):

1. Use web search to find action documentation
2. Verify required inputs and version
3. Check for deprecation warnings
4. Run validation script

Search format: "[action-name] [version] github action documentation"

Reference File Consultation Guide

MANDATORY Reference Consultation

Script Output to Reference Mapping

Reference Files Summary

Troubleshooting

Debug Mode

actionlint -verbose .github/workflows/ci.yml  # Verbose actionlint
act -v                                         # Verbose act
act -n                                         # Dry-run (no execution)

Best Practices

1. Always validate locally first - Catch errors before pushing
2. Use actionlint in CI/CD - Automate validation in pipelines
3. Pin action versions - Use @v6 not @main for stability; SHA pinning for security
4. Keep tools updated - Regularly update actionlint and act
5. Use web search for unknown actions - Verify usage with documentation
6. Check version compatibility - See references/action_versions.md
7. Enable shellcheck - Catch shell script issues early
8. Review security warnings - Address script injection issues

Limitations

• act limitations: Not all GitHub Actions features work locally
• Docker requirement: act requires Docker to be running
• Network actions: Some GitHub API actions may fail locally
• Private actions: Cannot validate without access
• Runtime behavior: Static analysis cannot catch all issues
• File location: act can only validate workflows in .github/workflows/ directory; files outside (like examples/) can only be validated with actionlint

Quick Examples

Example 1: Pre-commit Validation

cd .claude/skills/github-actions-validator
bash scripts/validate_workflow.sh .github/workflows/
git add .github/workflows/ && git commit -m "Update workflows"

Example 2: Debug Failing Workflow

bash scripts/validate_workflow.sh --lint-only .github/workflows/failing.yml
# Fix issues
bash scripts/validate_workflow.sh .github/workflows/failing.yml

Complete Worked Example: Multi-Error Workflow

This example demonstrates the full assistant workflow for handling multiple errors.

User's Problematic Workflow

name: Broken CI
on:
  schedule:
    - cron: '0 0 * * 8'  # ERROR 1
jobs:
  build:
    runs-on: ubuntu-lastest  # ERROR 2
    steps:
      - uses: actions/checkout@v3  # ERROR 3 (outdated)
      - run: echo ${{ github.event.issue.title }}  # ERROR 4 (security)
  deploy:
    needs: biuld  # ERROR 5 (typo)
    runs-on: ubuntu-latest
    steps:
      - run: echo "Deploying"

Step 1: Run Validation

bash scripts/validate_workflow.sh --lint-only workflow.yml

Output:

[ERROR] invalid CRON format "0 0 * * 8"
[ERROR] label "ubuntu-lastest" is unknown
[WARN] "github.event.issue.title" is potentially untrusted
[ERROR] job "deploy" needs job "biuld" which does not exist

Step 2-3: Consult References and Quote Fixes

Error 1: Invalid CRON Expression

From references/common_errors.md - Schedule Errors:

Cause: Day of week 8 doesn't exist (valid: 0-6, where 0 = Sunday)

# Bad
schedule:
  - cron: '0 0 * * 8'  # Day 8 doesn't exist

# Good
schedule:
  - cron: '0 0 * * 0'  # Sunday

CRON format: minute hour day month weekday

• Weekday: 0-6 (0 = Sunday)

Fix: Change 8 to 0 (Sunday) or 1-6 for Monday-Saturday.

Error 2: Invalid Runner Label

From references/common_errors.md - Job Configuration Errors and references/runners.md:

Cause: Typo in runner label

# Bad
runs-on: ubuntu-lastest  # Typo

# Good
runs-on: ubuntu-latest

Valid labels (from references/runners.md):

• ubuntu-latest (Ubuntu 24.04)
• ubuntu-24.04, ubuntu-22.04
• macos-latest (macOS 15)
• windows-latest (Windows Server 2022)

Fix: Change ubuntu-lastest to ubuntu-latest.

Error 3: Outdated Action Version

From references/action_versions.md:

Action	Current Version	Minimum Supported
actions/checkout	v6	v4

SHA Pinning Best Practice:

# Recommended: SHA pinning with version comment
- uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3  # v6.0.0

Fix: Update from @v3 to @v6 (or SHA-pinned version).

Error 4: Security Vulnerability (Script Injection)

From references/common_errors.md - Expression Errors:

Warning: Potential script injection via untrusted input

# Bad - vulnerable to injection
run: echo ${{ github.event.issue.title }}

# Good - use environment variables
env:
  TITLE: ${{ github.event.issue.title }}
run: echo "$TITLE"

Why: Untrusted input (issue titles, PR bodies, commit messages) can contain malicious commands. Using environment variables sanitizes the input.

Fix: Pass untrusted input through environment variable.

Error 5: Undefined Job Dependency

From references/common_errors.md - Job Configuration Errors:

Error: Job 'deploy' depends on job 'biuld' which does not exist

# Bad
jobs:
  build:
    runs-on: ubuntu-latest
  deploy:
    needs: biuld  # Typo

# Good
jobs:
  build:
    runs-on: ubuntu-latest
  deploy:
    needs: build

Fix: Change biuld to build.

Step 4: Provide Corrected Workflow

name: Fixed CI
on:
  schedule:
    - cron: '0 0 * * 0'  # Fixed: Sunday (0-6 valid)
jobs:
  build:
    runs-on: ubuntu-latest  # Fixed: typo corrected
    steps:
      - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3  # v6.0.0 - Fixed: updated version
      - name: Process issue
        env:
          TITLE: ${{ github.event.issue.title }}  # Fixed: use env var
        run: echo "$TITLE"
  deploy:
    needs: build  # Fixed: typo corrected
    runs-on: ubuntu-latest
    steps:
      - run: echo "Deploying"

Step 5: Summary

Recommendations:

• Run bash scripts/validate_workflow.sh --check-versions regularly
• Use SHA pinning for all actions in production workflows
• Always pass untrusted input through environment variables

Summary

1. Setup: Install tools with install_tools.sh
2. Validate: Run validate_workflow.sh on workflow files
3. Fix: Address issues using reference documentation
4. Test: Verify locally with act (when possible)
5. Search: Use web search to verify unknown actions
6. Commit: Push validated workflows with confidence

For detailed information, consult the appropriate reference file in references/.