What is listen?

Listen is a tool for Ruby that watches your folders for changes and tells your program whenever a file is added, modified, or deleted. This is what powers live-reloading tools, when you save a file, your browser automatically refreshes or your tests instantly re-run, saving you from manually switching windows and hitting refresh all day. At a high level, you point the tool at one or more directories and provide a short script, a "callback", that says what to do when a change happens. It then sits quietly in the background. When it notices a file change, it hands your script a list of exactly which files were modified, added, or removed. You can also fine-tune what it watches, telling it to ignore certain file types (like temporary logs) or to only track specific files (like your source code). Under the hood, it uses fast, built-in operating system features on Mac and Linux to get instant notifications with minimal performance impact. On other setups or certain network drives, it falls back to "polling", repeatedly checking the files for changes, which is slower but works everywhere. The project is currently looking for new maintainers to take over its ongoing development. A wide range of people use this, mostly behind the scenes. If you are building a developer tool, a static website generator, or an automated testing suite, you need a reliable way to trigger actions when files change. For example, a web developer might use it to automatically compile fresh stylesheets the moment they save a design file, or a data team might use it to trigger a data processing script the second a new CSV lands in a directory.