Hi Matoro342,
basically you hook the SetItem method of ItemTooltip and you are at the right place already.
This method is called to show the tooltip of an item, including the player's inventory.
You get the itemLink, you can get the itemId from it with GetItemLinkItemId. (and all other information, like style, from it)
Take a look at
https://www.esoui.com/downloads/info...eTooltips.html and feel free to use the code to start with.