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Act

Run GitHub Actions locally for fast feedback

open sourceupdated Aug 16, 2026

Act is an open-source tool that runs GitHub Actions workflows locally using Docker containers that match GitHub's execution environment. It provides instant feedback on workflow changes without pushing to a repository, supports matrix builds, secret management, and artifact handling. Act can also replace Makefiles by using workflow files as task definitions, making it useful for both CI/CD development and local task automation across development teams.

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Act solves one of the most frustrating parts of GitHub Actions development: the slow feedback loop of push-wait-check-fix cycles. Instead of committing and pushing every workflow change to see if it works, Act runs the entire Actions pipeline locally in Docker containers that replicate GitHub's hosted runner environment. Developers get immediate results for syntax errors, step ordering issues, and logic problems without waiting for remote CI to spin up.

The tool supports the full range of GitHub Actions features including matrix builds for testing across multiple configurations, encrypted secrets management, step-level conditionals, and artifact upload and download. Act reads standard workflow YAML files from the .github/workflows directory and executes them with the same semantics as GitHub's runner infrastructure. It also works as a general-purpose task runner, replacing Makefiles with the familiar workflow syntax that teams already know from their CI configuration.

With nearly 70,000 GitHub stars, Act has become an essential part of the DevOps toolkit for teams using GitHub Actions. It supports custom runner images, event simulation for triggers like push, pull_request, and workflow_dispatch, and can be configured to use smaller images for faster execution when full environment fidelity is not required. The tool is distributed under an MIT license and runs on macOS, Linux, and Windows wherever Docker is available.

Pricing

Free and open source under MIT license

Platforms

macOS, Linux, Windows — requires Docker

Categories

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FAQ

What is Act?

Act is an open-source tool that runs GitHub Actions workflows locally using Docker containers that match GitHub's execution environment. It provides instant feedback on workflow changes without pushing to a repository, supports matrix builds, secret management, and artifact handling. Act can also replace Makefiles by using workflow files as task definitions, making it useful for both CI/CD development and local task automation across development teams.

Is Act free?

Yes — Act is open source and free to use. Free and open source under MIT license

Is Act open source?

Yes — Act is open source.

What are the best Act alternatives?

The top editor-verified Act alternatives are GitHub Actions, GitLab CI/CD.

How does Act score in our review?

Our hands-on review scores Act 90/100 overall, based on speed, privacy, and developer-experience testing.