> [!CAUTION]
> **Important:** Chrome will be removing support for Chrome Apps on all platforms. Chrome browser and the Chrome Web Store will continue to support extensions. [**Read the announcement**](https://blog.chromium.org/2020/08/changes-to-chrome-app-support-timeline.html) and learn more about [**migrating your app**](https://developer.chrome.com/apps/migration).

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

> [!NOTE]
> **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](https://developer.chrome.com/extensions/overview#relative-urls) and [extension.getURL](https://developer.chrome.com/docs/apps/reference/extension#method-getURL).

To get a suitable key value, first install your extension from a `.crx` file (you may need to
[upload your extension](https://chrome.google.com/webstore/developer/dashboard) or [package it manually](https://developer.chrome.com/docs/extensions/how-to/distribute/host-on-linux.md.txt)). Then, in your [user data directory](https://www.chromium.org/user-experience/user-data-directory),
look in the file `Default/Extensions/_<extensionId>_/_<versionString>_/manifest.json`. You will see
the key value filled in there.