Minecraft wiki entry for Anvil_mechanics, associated text: The anvil can be used to combine two items of the same type and material, or an item with an enchanted book. This applies only to items with durability: weapons, shields, tools, and armor, as well as enchanted books. The first/left item is the target item, the second/right item is the sacrifice item, which is destroyed. Combining two similar items does either or both of two things. Each of these costs levels, but if they're both done at once, part of the cost is shared: