Minecraft wiki entry for Diamonds, associated text: Repairing two tools doesn't just add their durability up — it adds some extra uses as well (5% bonus for grindstone and 12% for anvils). That can help extend mining trips with non-enchanted tools. An anvil combines two identical equipment and their enchantments together, while doing it in a crafting menu loses all enchantments. (Durability also combined, enchanted or not) And depending on the target's enchantment level, it can get very expensive. An anvil can also repair equipment if so needed by sacrificing experience and equipment material. However, if a piece of equipment is repaired too many times with its material, it gets ridiculously expensive. To resolve this simply combine the target equipment with a piece of enchanted identical equipment, in which the enchant level should be as low as possible, in order to lower the experience needed. The dupe equipment could come from the player or from villager trading. A crafting-grid repair wipes enchantments, making way for a higher enchantment if the player needs it, but it is recommended to use a grindstone to gain some experience back. Repairing armor on an anvil with regular diamonds also uses fewer diamonds, but costs experience.