Unbreaking

How does it reduce wear?

For tools and weapons, a durability use is applied with probability 1 divided by level plus one: Unbreaking I, II and III ignore durability loss 50%, about 66.7% and 75% of the time. The expected lifetime is therefore about 2, 3 or 4 times the unenchanted baseline. Armor uses a different rule: the chance of losing durability is 80%, about 73.3% and 70% at levels I, II and III, corresponding to expected lifetimes around 1.25, 1.36 and 1.43 times baseline.

Which equipment benefits?

The supported list spans many durable items, including tools, weapons, armor, bows, crossbows, shields, fishing rods and elytra. The durability rule depends on the equipment category: do not use the tool/weapon lifetime multiplier to estimate armor's benefit. When a single use can cost several durability points, the reading says Unbreaking is evaluated for each point.

How should I prioritize levels?

Level III is the cap and offers the strongest durability preservation. It is especially useful on items you use often or whose replacement is inconvenient. The gains are larger in expected lifetime for non-armor items than for armor, so choose levels with that category difference in mind rather than assuming the same percentage benefit on every item.

What does it not do?

Unbreaking does not prevent all durability loss: even at level III, armor loses durability on 70% of qualifying uses, and non-armor items still lose it on one quarter of uses. It preserves durability rather than repairing it, so the item still wears down over time.

Limitations and tradeoffs

• Extends expected lifespan but never makes equipment immune to wear.
• Armor receives a smaller relative lifetime increase than tools and weapons.
• Higher levels improve the odds of avoiding durability loss, up to III.