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.

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-to-Reference Mapping

Error Pattern / Output Category	Reference File	Section to Consult
runs-on:, runner, ubuntu, macos, windows	references/runners.md	Runner labels
cron, schedule / [SCHEDULE]	references/common_errors.md	Schedule Errors
${{, expression, if: / [EXPRESSION]	references/common_errors.md	Expression Errors
needs:, job, dependency / [SYNTAX]	references/common_errors.md	Job Configuration Errors
uses:, action, input / [ACTION]	references/common_errors.md	Action Errors
untrusted, injection, security / [SECURITY]	references/common_errors.md	Script Injection section
syntax, yaml, unexpected	references/common_errors.md	Syntax Errors
docker, container / [DOCKER]	references/act_usage.md	Troubleshooting
[ACT-LIMIT], act fails but GitHub works	references/act_usage.md	Limitations
@v3, @v4, deprecated, outdated	references/action_versions.md	Version table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
User asks about actionlint config	references/actionlint_usage.md	Provide examples
Runner questions/errors	references/runners.md	Labels and availability

Quick Start

Initial Setup

cd .claude/skills/github-actions-validator
bash scripts/install_tools.sh  # Installs act and actionlint to scripts/.tools/

Validation Commands

# Full validation (lint + test)
bash scripts/validate_workflow.sh .github/workflows/ci.yml

# Lint-only (fastest, no Docker required)
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/ci.yml

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

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

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

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 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 scripts/install_tools.sh
"Docker daemon not running"	Start Docker or use --lint-only
"Permission denied"	Run chmod +x 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)

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 assets/) 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

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 to User

Using the Error-to-Reference Mapping table above, consult the relevant reference file for each error and quote the fix to the user:

#	Error	Reference File	Fix
1	invalid CRON format "0 0 * * 8"	common_errors.md - Schedule Errors	Change 8 to 0 (weekday range is 0–6)
2	label "ubuntu-lastest" is unknown	common_errors.md + runners.md	Change to ubuntu-latest
3	checkout@v3 (outdated)	action_versions.md	Update to @v6 or SHA-pinned equivalent
4	Untrusted input in run:	common_errors.md - Script Injection	Pass through environment variable
5	needs: biuld (typo)	common_errors.md - Job Configuration	Change to needs: build

Step 4: Corrected Workflow

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

Step 5: 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 scripts/validate_workflow.sh --check-versions regularly
• Use SHA pinning for all actions in production workflows
• Always pass untrusted input through environment variables

Anti-Patterns

NEVER skip lint-only mode when Docker is unavailable

• WHY: Skipping validation entirely because Docker is not installed leaves syntax errors, schema violations, and security issues undetected. actionlint catches the majority of real errors without Docker.
• BAD: Skip all validation when Docker is not installed.
• GOOD: Run --lint-only mode which covers syntax, schema, and security checks without requiring a container runtime.

NEVER ignore script injection warnings from actionlint

• WHY: Script injection warnings flag real attack vectors. Untrusted github.event.* values interpolated directly into shell commands allow a pull request author to execute arbitrary code in your workflow.
• BAD: Dismiss SC2086 or script injection warnings as low priority and merge anyway.
• GOOD: Pass untrusted input through environment variables — env: PR_TITLE: ${{ github.event.pull_request.title }} — then reference "$PR_TITLE" in the run: step.

NEVER validate a workflow file in isolation when it uses workflow_call or matrix

• WHY: Reusable workflows and matrix strategies depend on caller-provided inputs and context that cannot be resolved by validating the file alone. Skipping caller validation misses entire classes of type and expression errors.
• BAD: Validate only the reusable workflow file without also validating the calling workflow.
• GOOD: Validate both the caller and callee; note any warnings that require runtime context that static analysis cannot resolve.

NEVER accept deprecation warnings as harmless

• WHY: Deprecated action major versions (e.g., @v2 when @v4 is current) may receive no security patches. A known vulnerability in a deprecated version is an open door into your CI environment.
• BAD: Leave actions/checkout@v2 in place after the validator warns it is outdated.
• GOOD: Update to the current SHA-pinned version from references/action_versions.md.

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

References

Topic	Reference	When to Use
actionlint error patterns with explanations and fixes	Common Errors	Diagnosing a specific actionlint error message
Runner labels, availability, and hardware specs	Runners	Choosing or validating a runs-on label
Current version table for popular actions with SHA pins	Action Versions	Updating a deprecated or unpinned action reference
Local workflow testing with act, limitations and workarounds	act Usage	Running workflows locally before pushing
actionlint configuration and custom rule examples	actionlint Usage	Configuring actionlint or adding custom ignore rules
Modern GHA features: job summaries, environments, containers	Modern Features	Validating workflows that use newer GitHub Actions APIs