nektos/act

act is a command-line tool that lets you run your GitHub Actions workflows directly on your own machine, without having to push code to GitHub and wait for remote runners to execute them. It solves the slow feedback loop that developers face when debugging or tweaking .github/workflows/ files, instead of committing, pushing, waiting, and reading logs on GitHub, you can test your workflows instantly, locally. The way it works is straightforward: when you run act in a repository, it reads your workflow files from the .github/workflows/ directory, figures out which actions need to run and in what order (based on dependencies you've defined), then uses Docker to pull or build the container images each action requires. It then runs each step inside those containers, replicating the environment variables and filesystem layout that GitHub's own hosted runners provide. This means your local test environment closely mirrors what GitHub would actually execute. There are two main reasons to use it. First, for fast feedback during development: rather than treating every small workflow tweak as a full commit-and-push cycle, you can iterate locally in seconds. Second, as a general task runner: since GitHub Actions workflows are just structured YAML scripts, act lets you use them as a replacement for a Makefile or similar build tool, running tasks like tests, builds, or linters directly from the command line. You would reach for act whenever you're authoring or debugging CI workflows, want to test a workflow change before it touches the remote repository, or simply want to reuse your existing action definitions as a local automation layer. There is also a Visual Studio Code extension called GitHub Local Actions that integrates act directly into the editor. The tool is written in Go and depends on Docker being installed and running on your machine.