diff --git a/src/durability.lua b/src/durability.lua
new file mode 100644
index 0000000..17929b4
--- /dev/null
+++ b/src/durability.lua
@@ -0,0 +1,127 @@
+-- Weapon, armor and bow wear: unlike digging.lua's pick, a single limited-use
+-- tool discarded outright once spent, a piece of gear wears down from
+-- ordinary use but survives reaching zero - it just stops contributing to
+-- combat until repaired, exactly like disenchanting a rune off a weapon
+-- strips its bonus without destroying the weapon itself (see crafting.lua).
+-- A weapon or armor's power is baked straight into the wielder's
+-- attack/defense the instant it is equipped (see items.lua's
+-- Items.equipWeapon/equipArmor), so breaking or repairing one here adjusts
+-- that same baked total by the identical delta swapping gear already uses -
+-- never a separate "effective power" read live in combat. A bow is the one
+-- exception: its power is read live at the point of firing (see
+-- ranged.lua's Ranged.fire), so Durability.effectivePower covers that
+-- instead. Only the player's own gear wears at all - monsters have no
+-- inventory management or repair access, so wear is never applied to theirs.
+
+local Durability = {}
+
+Durability.MAX = 30
+Durability.WEAR_PER_HIT = 1
+Durability.REPAIR_COST_PER_POINT = 2
+
+-- Lazily stamps a fresh durability pair onto `item` the moment anything
+-- first asks about it, so an item built before this field existed on it
+-- (a raw table assembled somewhere this module cannot see) still gets a
+-- sensible default rather than an error.
+function Durability.ensure(item)
+  if not item.durability then
+    item.durability = Durability.MAX
+    item.maxDurability = Durability.MAX
+  end
+  return item
+end
+
+function Durability.isBroken(item)
+  Durability.ensure(item)
+  return item.durability <= 0
+end
+
+-- A broken bow contributes nothing to a shot's damage; read live in
+-- Ranged.fire in place of a bare `bow.power`.
+function Durability.effectivePower(item)
+  if not item then return 0 end
+  if Durability.isBroken(item) then return 0 end
+  return item.power or 0
+end
+
+local function isPlayerOwned(entity)
+  return entity.kind == "player"
+end
+
+-- Wears one point off `entity.weapon`, subtracting its power out of
+-- entity.attack the instant it actually breaks (never before, and never
+-- twice for the same break). A no-op, nil return, for an unarmed entity or
+-- one whose weapon already sits at zero.
+function Durability.wearWeapon(entity)
+  local item = entity.weapon
+  if not item then return nil end
+  Durability.ensure(item)
+  if item.durability <= 0 then return nil end
+  item.durability = item.durability - Durability.WEAR_PER_HIT
+  if item.durability <= 0 then
+    entity.attack = entity.attack - item.power
+    return isPlayerOwned(entity) and ("your " .. item.name .. " breaks apart from wear")
+      or (entity.name .. "'s " .. item.name .. " breaks apart from wear")
+  end
+  return nil
+end
+
+function Durability.wearArmor(entity)
+  local item = entity.armor
+  if not item then return nil end
+  Durability.ensure(item)
+  if item.durability <= 0 then return nil end
+  item.durability = item.durability - Durability.WEAR_PER_HIT
+  if item.durability <= 0 then
+    entity.defense = entity.defense - item.power
+    return isPlayerOwned(entity) and ("your " .. item.name .. " is battered to uselessness")
+      or (entity.name .. "'s " .. item.name .. " is battered to uselessness")
+  end
+  return nil
+end
+
+-- A bow's power is never baked into attack, so breaking one touches no stat
+-- - Ranged.fire simply stops reading any power out of it via
+-- Durability.effectivePower.
+function Durability.wearBow(entity)
+  local item = entity.bow
+  if not item then return nil end
+  Durability.ensure(item)
+  if item.durability <= 0 then return nil end
+  item.durability = item.durability - Durability.WEAR_PER_HIT
+  if item.durability <= 0 then
+    return isPlayerOwned(entity) and ("your " .. item.name .. " snaps from wear")
+      or (entity.name .. "'s " .. item.name .. " snaps from wear")
+  end
+  return nil
+end
+
+function Durability.missing(item)
+  Durability.ensure(item)
+  return item.maxDurability - item.durability
+end
+
+function Durability.repairCost(item)
+  return Durability.missing(item) * Durability.REPAIR_COST_PER_POINT
+end
+
+-- Spends `entity.gold` to restore `entity`'s gear in `slotName` (one of
+-- "weapon", "armor", "bow") fully, folding its power back into attack or
+-- defense if the break had already stripped it out. Fails without spending
+-- anything for an empty slot, an already-pristine item, or too thin a purse.
+function Durability.repair(entity, slotName)
+  local item = entity[slotName]
+  if not item then return false, "nothing equipped there" end
+  Durability.ensure(item)
+  if item.durability >= item.maxDurability then return false, "already in perfect condition" end
+  local cost = Durability.repairCost(item)
+  if entity.gold < cost then return false, "not enough gold" end
+  local wasBroken = item.durability <= 0
+  entity.gold = entity.gold - cost
+  item.durability = item.maxDurability
+  if wasBroken and slotName == "weapon" then entity.attack = entity.attack + item.power end
+  if wasBroken and slotName == "armor" then entity.defense = entity.defense + item.power end
+  return true, cost
+end
+
+return Durability