Act vs Black

act is an open-source command-line tool that runs GitHub Actions workflows locally using Docker containers. It reads workflow files from .github/workflows/ and executes them with environment variables and filesystem configurations matching GitHub's hosted runners. The tool enables fast local feedback on workflow changes without requiring commits and pushes to a remote repository.

Black is an opinionated Python code formatter that enforces a consistent style by reformatting entire files. It is deterministic, fast, and designed to end debates about code formatting by providing minimal configuration options.