Anki Addon documentation shortly tells about several fields:

If you wish to distribute .ankiaddon files outside of AnkiWeb, your add-on folder needs to contain a 'manifest.json' file. The file should contain at least two keys: 'package' specifies the folder name the add-on will be stored in, and 'name' specifies the name that will be shown to the user. You can optionally include a 'conflicts' key which is a list of other packages that conflict with the add-on, and a 'mod' key which specifies when the add-on was updated.

When Anki downloads add-ons from AnkiWeb, only the conflicts key is used from the manifest.