Anvil mechanics



This page explains the mechanics of the anvil. The anvil is primarily used to repair tools, armor, and weapons, which it can do without stripping their enchantments. It can also be used to combine the enchantments of two items, to give an item an individual name, or to crush other players that walk beneath it while it is falling. All its functions, except for crushing players, cost experience levels, and some have material costs.

The anvil has five basic functions: Renaming items can be done in the same work step as repairing or combining, provided the experience cost is not too high. In survival mode, the anvil can only apply 39 levels worth of work in a single operation. If the job would cost 40 or more levels, it will be rejected as "Too Expensive!". This does not apply in creative mode.
 * Renaming any item, including normal blocks. Note that blocks lose the rename when placed.
 * Repairing a "tiered" item with units of its material. For example, iron ingots can be used to repair iron tools and armor. Acceptable items for repair have the material to use in their default name, except for chainmail which is repaired with iron ingots.
 * Combining two items of the same kind and material that have durability, e.g. iron pickaxes, bows, shears, etc. The durabilities will combine similar to using a crafting table, and the enchantments are combined following rules detailed below.
 * Combining a tool with an enchanted book to add the book's enchantment to the tool. This costs much less than combining enchantments from two similar items, and can give enchantments to items that they could not get at an enchanting table.
 * Crushing any players who happen to walk under or be under the anvil while it is falling.

Prior Work penalty
Regardless of the work being done, be it rename, repair, or combine, there will be an extra cost to work on an item which has previously been altered in an anvil—the "prior work penalty". When an item is new, this value is zero.

Each time an item is worked on an anvil, even if only a rename (not applicable as of 1.9), its prior work penalty is multiplied by 2 and 1 is added. Thus, if an item has been worked N times the penalty will be 2^N - 1. After six workings, the penalty will be 63 levels, making any further repair or enchantment impossible in survival. After 31 workings, the penalty will be 2147483647 levels and further workings will be impossible in any mode (with one exception).

When combining two items, you pay both their penalties for the repair. The penalty on the resulting item is based on the input item with the higher penalty. For example, combining items with penalties 3 and 15 will pay a penalty of 18, and the combined item will have a penalty of 31 (15*2+1).

This penalty even applies to items which do not take damage, like enchanted books. Thus, combining 4x Fortune I books to create a single Fortune III book will result in a penalty of 3.

Renaming
Renaming always costs a single level, in addition to any Prior Work penalty. Renaming will increase the prior work penalty. As of 1.9, Renaming will not increase the penalty.

If the item is being renamed only, without being repaired or enchanted, the maximum level cost is 39 levels even if the Prior Work penalty is higher. However, the penalty is still increased as usual, and once the penalty reaches or exceeds 2147483647 further renames will be impossible (with one exception).

Stackable items can be renamed as a stack, while paying a single prior work penalty and a single level for the rename. Note that renamed items in general will not stack with normal items, and renamed blocks lose their name when placed.

Unit repair
Repairing a "tiered" target item using units of its material restores up to 25% total durability per unit and costs 1 level per unit of material used in addition to any applicable Prior Work penalties.
 * The material to use is in the original name of the item, except for chainmail which uses iron ingots.
 * Materials include leather, wood plank, cobblestone, iron ingot, gold ingot, and diamond.
 * Common tools you cannot repair in this way include bow, flint and steel, shears, fishing rod, and carrot on a stick.
 * If the stack of raw material has been renamed, its prior work penalty will be paid once regardless of the number of units being used in the repair.
 * Due to the rapid increase in prior work penalty for each repair, it will generally be most effective to use an item almost to the breaking point and then repair using four units of raw material at once (or by combining with a newly crafted instance of the item).

Combining items
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: swords, 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 will be 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 will be shared:
 * The target will be repaired, adding the durability of the sacrifice plus a bonus of 12% of the maximum durability, up to the item's maximum durability. If the target item is undamaged, there will be no charge for repair, otherwise the cost is 2 levels.
 * If the sacrifice has enchantments, it will also try to combine the sacrifice's enchantments onto the target. Regardless of whether any enchantments on the target are actually changed, you will be charged based on the enchantments on the target and sacrifice. For each enchantment on the sacrifice:
 * If the target has the enchantment as well...
 * and the sacrifice level is greater, the target will be raised to the sacrifice's level.
 * and the sacrifice level is equal, the target gains one level, unless it is already at the maximum level for that enchantment.
 * and the sacrifice level is less, nothing changes on the target.
 * If the target does not have the enchantment, it will gain all levels of that enchantment, unless it already has an incompatible enchantment. Enchantments are incompatible if both are in one of the following groups:
 * Sword: Sharpness, Smite, and Bane of Arthropods
 * Tool: Fortune and Silk Touch
 * Armor: Protection, Fire Protection, Projectile Protection, and Blast Protection

The total cost for combining two similar items is the sum of:
 * Prior Work penalties of both target and sacrifice.
 * If renaming, the extra cost of renaming
 * If the target item is not at full durability, the repair cost of 2 levels.
 * If the sacrifice has enchantments, the enchantment cost.

If the sacrifice is a book there will be no repair, but the anvil will try to combine the book's enchantments onto the target. The item can also be renamed at the same time. The enchantment cost will generally be less than for combining two similar items.

Costs for combining enchantments
(This is just the enchanting cost. The total cost outline is in Combining items.)
 * For each enchantment on the sacrifice:
 * Ignore any enchantment that cannot be applied to the target (e.g. Protection on a sword).
 * Add one level for every incompatible enchantment on the target.
 * If the enchantment is compatible with the existing enchantments on the target, add the final level of the enchantment on the target item multiplied by the multiplier from the table below.

Examples:
 * Dealing with equal enchantments:
 * In the first slot, the target is a sword with Sharpness III, Knockback II, and Looting III.
 * In the second slot, the sacrifice is a sword with Sharpness III and Looting III.
 * For the Sharpness III enchantment on the sacrifice: Since the target has an equal level, add one to the target's Sharpness level giving Sharpness IV. Add 4 (multiplier 1 times 4 levels) to the level cost for Sharpness IV.
 * For the Looting III enchantment on the sacrifice: Since the maximum level for Looting is III, the target remains at Looting III. But 12 (multiplier 4 times 3 levels) is still added to the level cost.
 * Thus, the enchanting cost is 16. The total cost for the work will include any prior work penalties, repair costs, and rename costs.
 * If combined in the other order (the sword having three enchantments as the sacrifice), there would also be a cost of 4 (level 2 times multiplier 2) for the Knockback II enchantment, giving a total enchantment cost of 20 levels.
 * Dealing with unequal enchantments:
 * In the first slot, the target is a sword with Sharpness III, Knockback II, and Looting I.
 * In the second slot, the sacrifice is a sword with Sharpness I and Looting III.
 * For the Sharpness I enchantment on the sacrifice: Since the target has a higher level, the target keeps Sharpness III. But 3 (multiplier 1 times 3 levels) is still added to the level cost.
 * For the Looting III enchantment on the sacrifice: Since the target has a lower level, it is upgraded to Looting III. Add 12 (multiplier 4 times 3 levels) to the level cost.
 * Thus, the enchanting cost is 15. The total cost for the work will include any prior work penalties, repair costs, and rename costs.
 * If combined in the other order (the sword having three enchantments as the sacrifice), there would also be a cost of 4 (level 2 times multiplier 2) for adding the Knockback II enchantment, giving a total enchantment cost of 19 levels.
 * Dealing with conflicting enchantments:
 * In the first slot, the target is a sword with Sharpness II and Looting II.
 * In the second slot, the sacrifice is a sword with Smite V and Looting II.
 * For the Smite V enchantment on the sacrifice: Since Smite is incompatible with Sharpness, add 1 level. The target keeps Sharpness II.
 * For the Looting II enchantment on the sacrifice: Since the target has an equal level, add one to the target's Looting level giving Looting III. Add 12 (multiplier 4 times 3 levels) to the level cost for Looting III.
 * Thus, the enchanting cost is 13. The total cost for the work will include any prior work penalties, repair costs, and rename costs.
 * If combined in the other order (the Sharpness sword as the sacrifice), the cost would again be 13 with the result having Smite V and Looting III.
 * Using books:
 * In the first slot, the target is a sword with Looting II.
 * In the second slot, the sacrifice is a book with Protection III, Sharpness I, and Looting II.
 * For the Protection III enchantment on the sacrifice: Since Protection is incompatible with swords, ignore it.
 * For the Sharpness I enchantment on the sacrifice: Since the target has no Sharpness, it gets Sharpness I. Add 1 level (multiplier 1 times 1 level) for Sharpness I.
 * For the Looting II enchantment on the sacrifice: Since the target has an equal level, add one to the target's Looting level giving Looting III. Add 6 (multiplier 2 times 3 levels) to the level cost for Looting III.

Trivia

 * The technical reason items can no longer be worked once the prior work cost reaches 2147483647 is that that number is the maximum number that a 32-bit binary integer can represent (and thus the maximum possible value for Java variables declared as integers), and so adding even 1 (for a rename) overflows to -2147483648, and the anvil refuses to process work that costs less than 1 level.
 * This no longer applies in 1.9 since it's impossible to raise the cost further through renaming.
 * While renaming no longer resets the prior work cost, there is a ridiculously-expensive method (removed in 1.9) to do so for items with durability:
 * Rename the item repeatedly until it cannot be renamed any more (for a total cost of around 1000 levels).
 * Do the same with a second item (costing another 1000 levels).
 * Ensure the target item is damaged, if only by one use.
 * Combine the two and rename at the same time. The total cost will be 2147483647 prior work on the target + 2147483647 prior work on the sacrifice + 2 for the repair + 1 for the rename, totaling 4294967297 levels, which overflows to give a total cost of just 1 level. The prior work cost on the result will be -1, again due to overflow.
 * The above can also be done by renaming a stack of raw materials in step 2, and ensuring that the target item is lacking enough durability to require at least 2 units to repair in step 3. If 3 or 4 units are needed, the rename in step 4 may be omitted.
 * The item with prior work cost -1 must be worked in such a way that the final cost is at least 1 level (e.g. repaired by combining, or repaired using 2 or more units, or repaired with a single unit and renamed). The prior work cost of the result will depend on the item combined with, since -1 is likely to be less than the cost on the other item. Combining two items with a -1 prior work cost will give a result with a -1 cost.
 * Enchantments that are added to raw materials (e.g. an Iron Ingot with Sharpness III) are ignored when doing unit repair, not combined.