Github Act

Run GitHub Actions Locally with gh act

Use gh act to run .github/workflows jobs locally before pushing. This is useful for fast CI iteration in any repository.

Setup

Install the extension once:

gh extension install https://github.com/nektos/gh-act

Check available options:

gh act --help

gh act requires a running container runtime (typically Docker).

Quick Commands

# List discovered workflows/jobs
gh act -l

# Run the default event (usually push)
gh act

# Run a specific event
gh act push
gh act pull_request
gh act workflow_dispatch

# Run one job by job id
gh act pull_request -j test

# Restrict to one workflow file
gh act pull_request -W .github/workflows/ci.yml

CI Workflow Loop

# 1) Validate workflow syntax without creating containers
gh act -n --validate

# 2) Run only the failing job with verbose logs
gh act pull_request -j test -v

# 3) Re-run quickly while preserving container state
gh act pull_request -j test --reuse

Use --matrix to target one matrix entry while debugging:

gh act pull_request -j test --matrix os:ubuntu-latest --matrix shard:1

Inputs, Secrets, Vars, and Env

Pass values directly:

gh act workflow_dispatch \
  --input target=staging \
  --secret GITHUB_TOKEN="$(gh auth token)" \
  --var DEPLOY_REGION=us-east-1 \
  --env CI=true

Or load from files (defaults shown):

• .input via --input-file
• .secrets via --secret-file
• .vars via --var-file
• .env via --env-file

High-Value Flags

• -n, --dryrun: validate workflow/job planning without running containers
• --validate: strict workflow validation
• -v, --verbose: detailed logs
• --json: machine-readable logs
• -g, --graph: show workflow graph
• -w, --watch: rerun on file changes
• -C, --directory: run against another repository path
• -W, --workflows: choose workflow file(s) or directories
• -P, --platform: override runner image mapping
• --pull, --action-offline-mode: control image/action refresh behavior

Troubleshooting

• If ubuntu-latest image resolution fails, provide explicit mapping with -P.
• If secrets are missing, pass with --secret or provide .secrets.
• If a workflow depends on GitHub-hosted services, local runs may need mocks or conditional steps.
• Use gh act -l first to confirm job ids before -j <job-id>.

Source: krastanov/juliallmagentskills — distributed by TomeVault.