I can add a custom resource tool to the detail view of a resource.
The Laravel Nova Docs say:
... resource tools are displayed on a particular resource's detail screen
How can I add the resource tool to the index view of a resource?
Resource tools are specifically for a single resource..
If you want to display a custom component above the resource index.. Create a custom card
If you want the entire page without the resource table below it.. Create a custom tool
You can also package tools, resource tools and cards in the same package and share assets.