This is the source code to my minecraft mod Runesword, which adds a new type of item to the game, called runes, which can be dropped by mobs and found in treasure chests. These runes can be applied to swords and axes, via the use of a new crafting station called the runeforge. These runes grants the sword/axe bonuses, such as extra damage underwater, or giving the player a speed boost on kill.

As of mod version 1.4.0, item tags are used to determine what rune powers an item should get, and how many runes an item can equip. This means that you can use a datapack to extend/change which items can equip runes. See this and this for the default tag values.