What it does
act is a command-line tool that reads workflow files from `.github/workflows` and runs jobs locally. It uses the Docker Engine API to prepare runner images and execute workflow steps, so developers can try event-triggered workflows without pushing each edit to GitHub. It is a local testing and task-running aid, not GitHub's hosted Actions service or a replacement for checking the actual hosted runner.
In a repository that already has GitHub Actions workflows, install act and make sure Docker Engine is available. Its usage guide documents act push for workflows triggered by a push and act -l pull_request for listing workflows that match a pull-request event. If a job depends on event-specific fields, provide a payload file instead of assuming local defaults reproduce a real GitHub event. Those are documented examples, not commands run for this listing.
The output is local job execution and step logs, which can expose workflow mistakes before a commit-and-push cycle. Use it for quick feedback, then keep the normal hosted or self-hosted Actions run as the final check when runner details matter. The default images are intentionally incomplete compared with GitHub-hosted environments, and containers do not reproduce every virtual-machine behavior. Docker images and local compute are separate dependencies whose cost depends on the operator.
Strengths
- Runs existing `.github/workflows` locally rather than requiring a push for every workflow edit.
- Supports choosing a GitHub event and listing workflows that match it.
- Prebuilt executables are documented for Linux, macOS, and Windows.
Watch out for
- Container-based runs require Docker Engine; other container backends are not officially supported.
- Default runner images are incomplete and local containers do not fully reproduce GitHub's virtual machines.
Best for
- Trying a GitHub Actions workflow change before pushing it
- Reproducing a push or pull-request job locally during development
- Using repository workflow files as local repeatable tasks
Sources
- Introduction - act - User Guide | Manual | Docs | Documentation (Oct 25, 2026)
- Installation - act - User Guide | Manual | Docs | Documentation (Oct 25, 2026)
- Runners - act - User Guide | Manual | Docs | Documentation (Oct 25, 2026)
- Usage guide - act - User Guide | Manual | Docs | Documentation (Oct 25, 2026)
- nektos/act (Oct 25, 2026)
- act/LICENSE at master · nektos/act · GitHub (Oct 25, 2026)
- GitHub Actions documentation - GitHub Docs (Oct 25, 2026)