* **Fast Feedback** - Rather than having to commit/push every time you want to test out the changes you are making to your `.github/workflows/` files (or for any changes to embedded GitHub actions), you can use `act` to run the actions locally. The [environment variables](https://help.github.com/en/actions/configuring-and-managing-workflows/using-environment-variables#default-environment-variables) and [filesystem](https://help.github.com/en/actions/reference/virtual-environments-for-github-hosted-runners#filesystems-on-github-hosted-runners) are all configured to match what GitHub provides.
* **Local Task Runner** - I love [make](https://en.wikipedia.org/wiki/Make_(software)). However, I also hate repeating myself. With `act`, you can use the GitHub Actions defined in your `.github/workflows/` to replace your `Makefile`!
When you run `act` it reads in your GitHub Actions from `.github/workflows/` and determines the set of actions that need to be run. It uses the Docker API to either pull or build the necessary images, as defined in your workflow files and finally determines the execution path based on the dependencies that were defined. Once it has the execution path, it then uses the Docker API to run containers for each action based on the images prepared earlier. The [environment variables](https://help.github.com/en/actions/configuring-and-managing-workflows/using-environment-variables#default-environment-variables) and [filesystem](https://help.github.com/en/actions/reference/virtual-environments-for-github-hosted-runners#filesystems-on-github-hosted-runners) are all configured to match what GitHub provides.
GitHub Actions offers managed [virtual environments](https://help.github.com/en/actions/reference/virtual-environments-for-github-hosted-runners) for running workflows. In order for `act` to run your workflows locally, it must run a container for the runner defined in your workflow file. Here are the images that `act` uses for each runner type:
These default images do **not** contain **all** the tools that GitHub Actions offers by default in their runners.
## Alternative runner images
If you need an environment that works just like the corresponding GitHub runner then consider using an image provided by [nektos/act-environments](https://github.com/nektos/act-environments):
* [nektos/act-environments-ubuntu:18.04](https://hub.docker.com/r/nektos/act-environments-ubuntu/tags) - built from the Packer file GitHub uses in [actions/virtual-environments](https://github.com/actions/runner).
To run `act` with secrets, you can enter them interactively or supply them as environment variables. The following options are available for providing secrets:
*`act -s MY_SECRET=somevalue` - use `somevalue` as the value for `MY_SECRET`.
*`act -s MY_SECRET` - check for an environment variable named `MY_SECRET` and use it if it exists. If the environment variable is not defined, prompt the user for a value.
You can provide default configuration flags to `act` by either creating a `./.actrc` or a `~/.actrc` file. Any flags in the files will be applied before any flags provided directly on the command line. For example, a file like below will always use the `nektos/act-environments-ubuntu:18.04` image for the `ubuntu-latest` runner:
Additionally, act supports loading environment variables from an `.env` file. The default is to look in the working directory for the file but can be overridden by:
Every [GitHub event](https://developer.github.com/v3/activity/events/types) is accompanied by a payload. You can provide these events in JSON format with the `--eventpath` to simulate specific GitHub events kicking off an action. For example:
