- Alt - Shows the tooltip of an item on the ground, of the held item of another player or of an item in an item frame
- Ctrl - Shows the tooltip of the currently equipped item
- Shift - Shows the tooltip of the item that you're currently dragging in the inventory
You can change the positioning and the color of the tooltip in the config gui in the mod list.
Keep in mind that this is a client-side mod, installing it on a server will crash it
You can look at the source code here.