GitHub Actions Code Review Rules

Security (Critical)

• Pin actions to full commit SHA (not @v1 or @main)
• Use minimal permissions block (principle of least privilege)
• Never echo secrets or use them in URLs
• Use secrets.GITHUB_TOKEN instead of PATs when possible
• Audit third-party actions before use
• Review expressions (${{ }}) for injection risks; never interpolate untrusted user input
• Validate all inputs to reusable workflows and custom actions

Permissions

permissions:
  contents: read  # Minimal by default
  # Add only what's needed:
  # pull-requests: write
  # issues: write

Secrets

• Store secrets in repository/organization secrets
• Use environments for production secrets with approvals
• Don't pass secrets as command arguments (visible in logs)
• Mask sensitive output with ::add-mask::
• Never write secrets to files or artifacts (can be exposed)
• Avoid passing secrets via environment variables unless absolutely required
• Secrets in env vars can be visible in process listings

Performance

• Use caching for dependencies (actions/cache or built-in)
• Run independent jobs in parallel
• Use concurrency to cancel redundant runs
• Consider self-hosted runners for heavy workloads

Workflow Structure

• Use reusable workflows for common patterns
• Use composite actions for shared steps
• Set appropriate timeout-minutes to prevent hung jobs
• Use if: conditions to skip unnecessary jobs
• Separate CI (testing), CD (deployments), and PR checks into distinct workflows
• Use environments to distinguish between dev, staging, and production
• Avoid mixing all concerns in a single monolithic workflow

Triggers

• Be specific with paths and branches filters
• Use workflow_dispatch for manual triggers
• Consider pull_request_target security implications

Common Anti-patterns

• Avoid actions/checkout with persist-credentials: true unless needed
• Avoid running on push to all branches
• Avoid hardcoding versions that need updates

Action Updates and Maintenance

• Monitor pinned action SHAs for security fixes
• Subscribe to security advisories for actions you use
• Update actions regularly to get new features and fixes
• Document why specific SHAs are pinned (security, stability)
• Consider using Dependabot for action version updates

Testing and Validation

• Lint workflows with tools like actionlint
• Test complex workflows in feature branches before merging
• Validate workflow syntax before committing
• Use workflow templates for consistency
• Add job-level tests for workflow logic validation

Error Handling

• Use continue-on-error: false as default (explicit failure)
• Set fail-fast: true for matrix jobs to stop on first failure
• Only use continue-on-error: true when failure is acceptable
• Provide clear error messages in job outputs
• Use status checks to ensure critical jobs pass

Documentation

• Add inline comments for complex workflow logic
• Document workflow purpose and triggers
• Maintain workflow README or documentation
• Explain environment variables and their usage
• Document required secret names and their purpose (never include actual secret values)