Chrome Devtools

What are extensions? Chrome extensions enhance the browsing experience by customizing the user interface, observing browser events, and modifying the web. Visit the Chrome Web Store for more examples of what extensions can do.

How are they built? You can build extensions using the same web technologies that are used to create web applications: HTML, CSS, and JavaScript.

What can they do? In addition to Web APIs, extensions also have access to Chrome Extension APIs to accomplish different tasks. For a more detailed overview, take a look at the Develop guide.

The extension's manifest is the only required file that must have a specific file name: manifest.json. It also has to be located in the extension's root directory. The manifest records important metadata, defines resources, declares permissions, and identifies which files to run in the background and on the page.

A service worker runs in the background and handles browser events, like removing a bookmark, or closing a tab. They don't have access to the DOM, but you can combine it with an offscreen document for this use case.

Content scripts run JavaScript in the context of a web page.