act

act is a local runner for GitHub Actions workflows. It reads .github/workflows, plans jobs for an event or selected job, and executes them in Docker so you can test CI behavior before pushing.

• Run workflow jobs locally against a chosen event payload or job ID, with local secrets, vars, env files, matrix filters, and repository overrides.
• List workflows, inspect stage ordering as a graph, validate workflow definitions, and dry-run execution paths before spending CI time on GitHub-hosted runners.
• Iterate faster on workflows and custom actions with local caches, artifact or cache servers, and --watch reruns when files change.

• Once Docker access and runner image mappings are configured, commands are mostly non-interactive and fit inspect-change-verify loops around CI debugging.
• Structured output is limited but real: --json emits JSON logs and --list-options returns a JSON description of supported flags.
• Best for agents already operating inside a repo with GitHub Actions; it is less useful as a general GitHub control plane because behavior depends on local workflow fidelity and containerized runner support.

• Execution depends on Docker-compatible containers and suitable runner images, and the docs explicitly note that act is not completely compatible with GitHub runners.
• First run can prompt for a default image selection unless .actrc or explicit -P or --platform mappings are already in place.