The `manifest.json` file defines the app's constants, a bunch of values that YunoHost needs to identify the app and install it correctly. It looks like this:
* **description**: complete app description. You can make it as detailed as you feel it should be. Only `en` is required right now, but you can translate the description by prepending the locale prefix.
* **multi_instance**: this defines your app's ability to be installed multiple times. When YunoHost tries to install a second instance of the app, it will replace the `id` in the scripts by an `id__2`. It means that, if you want to be `multi_instance`, you have to put all the identifiers in the scripts.
<br/><br/>**E.g.** in the roundcube script, database is called `roundcube`, the install directory `roundcube` and the Nginx configuration `roundcube`. This way, the second instance of roundcube will not conflict with the first one, and will be installed in the `roundcube__2` database, in the `roundcube__2`directory, and with the `roundcube__2` Nginx configuration.