Tools are a category of items you can craft in your Crafting Menu (default key "Q").
These tools will go into the tool slot in your equipment to the left side of your characters' model next to the inventory/bag. They can be "readied" with the TAB key (as the default key) after being equipped. This key is called in the key setting menu and will cycle between Power Cell, Weapon and Tool if worn.
Even though Excavators can be found in your crafting-category Explosives and can be rendered useless by turning off the world-option to use area-damaging explosives, they could also be viewed as mining tools. However they cannot be equipped in the "tool" slot and aren't listed under "tools" in the crafting menu ingame.