You know back in the days, when you played GTA and used the cheat code for a tank, and then went on and caused mayhem? This mod is like that, except for tinker tools and the cheatcode takes longer to enter.
Gives your Tools XP, allowing them to level up. On levelup an extra modifier is rewarded. You get xp for doing whatever the tool was intended for, so breaking blocks with pickaxes, killing things with swords, etc.
Note that swords get xp relative to the damage dealt when the entity is killed, not when the damage is dealt. You only get xp if the mob is killed!