Agent Skills: GitHub Actions Validator

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.

Trigger Phrases

Use this skill when the request includes phrases like:

• "validate this GitHub Actions workflow"
• "check my .github/workflows/*.yml file"
• "debug actionlint errors"
• "test this workflow locally with act"
• "verify GitHub Action versions or deprecations"

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

Required Execution Flow

Every validation run should follow these steps in order.

Step 1: Set Skill Path and Run Validation

Run commands from the repository root that contains .github/workflows/.

SKILL_DIR="devops-skills-plugin/skills/github-actions-validator"
bash "$SKILL_DIR/scripts/validate_workflow.sh" <workflow-file-or-directory>

Step 2: Map Each Error to a Reference

For each actionlint/act error, consult the mapping table below, then extract the matching fix pattern.

Step 3: Apply Minimal-Quote Policy

For each issue:

1. Include the exact error line from tool output.
2. Quote only the smallest useful snippet from references/ (prefer <=8 lines).
3. Paraphrase the rest and cite the source file/section.
4. Show corrected workflow code.

Step 4: Handle Unmapped Errors Explicitly

If an error does not match any mapping:

1. Label it as UNMAPPED.
2. Capture exact tool output, workflow file, and line number (if available).
3. Check references/common_errors.md general sections first.
4. If still unresolved, search official docs with the exact error string.
5. Mark the fix as provisional until post-fix rerun passes.

Step 5: Verify Public Action Versions

For each uses: owner/action@version:

1. Check references/action_versions.md.
2. For unknown actions, verify against official docs.
3. Confirm required inputs and deprecations.

Offline mode behavior:

• If network/doc lookup is unavailable, rely on references/action_versions.md only.
• Mark unknown actions as UNVERIFIED-OFFLINE.
• Do not claim "latest" version without an online verification pass.

Step 6: Mandatory Post-Fix Rerun

After applying fixes, rerun validation before finalizing:

SKILL_DIR="devops-skills-plugin/skills/github-actions-validator"
bash "$SKILL_DIR/scripts/validate_workflow.sh" <workflow-file-or-directory>

Step 7: Provide Final Summary

Final output should include:

• Issues found and fixes applied
• Any UNMAPPED or UNVERIFIED-OFFLINE items
• Post-fix rerun command and result
• Remaining warnings/risk notes

Error Type to Reference File Mapping

| Error Pattern in Output | Reference File to Read | Section to Quote | |------------------------|----------------------|------------------| | runs-on:, runner, ubuntu, macos, windows | references/runners.md | Runner labels | | cron, schedule | references/common_errors.md | Schedule Errors | | ${{, expression, if: | references/common_errors.md | Expression Errors | | needs:, job, dependency | references/common_errors.md | Job Configuration Errors | | uses:, action, input | references/common_errors.md | Action Errors | | untrusted, injection, security | references/common_errors.md | Script Injection section | | syntax, yaml, unexpected | references/common_errors.md | Syntax Errors | | docker, container | references/act_usage.md | Troubleshooting | | @v3, @v4, deprecated, outdated | references/action_versions.md | Version table | | workflow_call, reusable, oidc | references/modern_features.md | Relevant section | | glob, path, paths:, pattern | references/common_errors.md | Path Filter Errors |

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

Set once per shell session:

SKILL_DIR="devops-skills-plugin/skills/github-actions-validator"

Initial Setup

bash "$SKILL_DIR/scripts/install_tools.sh"

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

Basic Validation

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

# Validate all workflows
bash "$SKILL_DIR/scripts/validate_workflow.sh" .github/workflows/

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

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

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

3. Full Validation

bash "$SKILL_DIR/scripts/validate_workflow.sh" .github/workflows/ci.yml

Default behavior if tools/runtime are unavailable:

• If act is missing, full validation falls back to actionlint-only.
• If Docker is unavailable, full validation skips act and continues with actionlint.
• --check-versions works in offline/local mode using references/action_versions.md.

Validating Resource Types

Workflows

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

# All workflows
bash "$SKILL_DIR/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 "$SKILL_DIR/scripts/validate_workflow.sh" .github/workflows/test-custom-action.yml

Public Actions

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

1. Check references/action_versions.md first
2. Use official docs (or web search) for unknown actions
3. Verify required inputs and version
4. Check for deprecation warnings
5. Run validation script

If offline:

• Mark unknown versions as UNVERIFIED-OFFLINE
• Avoid "latest/current" claims until online verification is possible

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

Reference File Consultation Guide

Mandatory Reference Consultation

| Situation | Reference File | Action | |-----------|---------------|--------| | actionlint reports any mapped error | references/common_errors.md | Find matching error and apply minimal quote policy | | actionlint reports unmapped error | references/common_errors.md + official docs | Label as UNMAPPED, capture exact output and verify by rerun | | act fails with Docker/runtime error | references/act_usage.md | Check Troubleshooting section | | act fails but workflow works on GitHub | references/act_usage.md | Read Limitations section | | User asks about actionlint config | references/actionlint_usage.md | Provide examples | | User asks about act options | references/act_usage.md | Read Advanced Options | | Security vulnerability detected | references/common_errors.md | Quote minimal safe fix snippet | | Validating action versions | references/action_versions.md | Check version table and offline note | | Using modern features | references/modern_features.md | Check syntax examples | | Runner questions/errors | references/runners.md | Check labels and availability |

Script Output to Reference Mapping

| Output Pattern | Reference File | |----------------|----------------| | [syntax-check], parse, YAML errors | common_errors.md - Syntax Errors | | [expression], ${{, condition parsing | common_errors.md - Expression Errors | | [action], uses:, input/output mismatch | common_errors.md - Action Errors | | [events] with CRON/schedule text | common_errors.md - Schedule Errors | | potentially untrusted, injection warnings | common_errors.md - Security section | | [runner-label] or unknown runs-on label | runners.md | | [job-needs] dependency errors | common_errors.md - Job Configuration Errors | | [glob], paths, pattern errors | common_errors.md - Path Filter Errors | | Docker/pull/image errors from act | act_usage.md - Troubleshooting | | No pattern match | common_errors.md + official docs (label UNMAPPED) |

Reference Files Summary

| File | Content | |------|---------| | references/act_usage.md | Act tool usage, commands, options, limitations, troubleshooting | | references/actionlint_usage.md | Actionlint validation categories, configuration, integration | | references/common_errors.md | Common errors catalog with fixes | | references/action_versions.md | Current action versions, deprecation timeline, SHA pinning | | references/modern_features.md | Reusable workflows, SBOM, OIDC, environments, containers | | references/runners.md | GitHub-hosted runners (ARM64, GPU, M2 Pro, deprecations) |

Troubleshooting

| Issue | Solution | |-------|----------| | "Tools not found" | Run bash "$SKILL_DIR/scripts/install_tools.sh" | | "Docker daemon not running" | Start Docker or use --lint-only | | "Permission denied" | Run chmod +x "$SKILL_DIR"/scripts/*.sh | | act fails but GitHub works | See references/act_usage.md Limitations |

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 official docs for unknown actions - Verify usage and versions
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

SKILL_DIR="devops-skills-plugin/skills/github-actions-validator"
bash "$SKILL_DIR/scripts/validate_workflow.sh" .github/workflows/
git add .github/workflows/ && git commit -m "Update workflows"

Example 2: Debug Failing Workflow

bash "$SKILL_DIR/scripts/validate_workflow.sh" --lint-only .github/workflows/failing.yml
# Fix issues
bash "$SKILL_DIR/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 "$SKILL_DIR/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: Mandatory Rerun

bash "$SKILL_DIR/scripts/validate_workflow.sh" --lint-only workflow.yml

Expected rerun result:

• No previous errors reproduced
• Remaining warnings, if any, are documented explicitly

Step 6: Summary

| Error | Type | Fix Applied | |-------|------|-------------| | CRON 0 0 * * 8 | Schedule | Changed to 0 0 * * 0 | | ubuntu-lastest | Runner | Changed to ubuntu-latest | | checkout@v3 | Outdated Action | Updated to @v6.0.0 (SHA-pinned) | | Direct ${{ }} in run | Security | Wrapped in environment variable | | needs: biuld | Job Dependency | Changed to needs: build |

Recommendations:

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

Done Criteria

Validation work is complete when all are true:

• Trigger matched and correct validation mode selected.
• Each mapped error includes source reference and minimal quote.
• Each unmapped error is labeled UNMAPPED with exact output captured.
• Public action versions are verified, or marked UNVERIFIED-OFFLINE.
• Post-fix rerun executed and result reported.

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. Rerun: Verify fixes with a mandatory post-fix validation run
5. Search: Use official docs to verify unknown actions
6. Commit: Push validated workflows with confidence

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