Manifest - Key
The Chrome Web Store no longer accepts Manifest V2 extensions. Please use Manifest V3 when building new extensions. You will find a section on upgrading in the navigation tree at the left, including the Manifest V2 support timeline.
This value can be used to control the unique ID of an extension, app, or theme when it is loaded during development.
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/EXTENSION_ID/EXTENSION_VERSION/manifest.json. You will see the key value filled in there.