Important: Chrome will be removing support for Chrome Apps on Windows, Mac, and Linux. Chrome OS will continue to support Chrome Apps. Additionally, Chrome and the Web Store will continue to support extensions on all platforms. Read the announcement and learn more about migrating your app.

Manifest - Key

This value can be used to control the unique ID of an extension, app, or theme when it is loaded during development.

Note: You don't usually need to use this value. Instead, write your code so that the key value doesn't matter by using relative paths and extension.getURL.

To get a suitable key value, first install your extension from a .crx file (you may need to upload your extension or package it manually). Then, in your user data directory, look in the file Default/Extensions/<extensionId>/<versionString>/manifest.json. You will see the key value filled in there.