wtf is changed-files?

Changed-files is a GitHub Action that figures out which files were added, modified, deleted, or renamed when someone pushes code or opens a pull request. Instead of running your entire test suite or rebuilding your whole project every time, you can use it to only run steps that are relevant to the files that actually changed. At a high level, it compares the current state of your code against the previous commit or the target branch of a pull request. You can ask it for a simple list of everything that changed, or you can filter by specific folders and file patterns. For example, you could tell it to only watch the "docs" folder, and it will return a true/false flag indicating whether anything in that folder was touched. It runs fast, typically in under two seconds, and works across Linux, macOS, and Windows. This is most useful for teams managing automated workflows on GitHub, especially those working with larger repositories or monorepos where different parts of the project live in the same repo. A practical example: if you have a monorepo with separate frontend and backend folders, you could use this action to only run frontend tests when files in the frontend folder change, skipping the backend tests entirely. That saves time and compute resources on every commit. It also supports filtering with glob patterns, so you can target something like "all YAML files in the config directory." The action provides a wide range of outputs, you can get lists of files grouped by change type (added, copied, modified, deleted, renamed, and so on), or simple boolean flags for whether specific files you care about were touched. It works with GitHub-hosted runners, self-hosted runners, and GitHub Enterprise Server. The README includes a usage example showing how to drop it into a workflow file alongside the standard checkout step, with a note that you need to set an appropriate fetch depth so the action has enough git history to compare against.