Items & Inventory

session.itemState is an ItemStateTracker — the local inventories, open containers and forms, the item registry, and the controller that moves/drops items.

ItemStateTracker

Member	Type	Description
controller	AbstractInventoryController	Moves/drops/consumes items (see below).
openContainer	AbstractDynamicInventory | null	The currently open container/inventory, if any.
openForm	Form | null	The currently open modal form, if any.
items	Map<number, ItemDefinition>	Item registry, keyed by network runtime id.
itemsByName	Map<string, ItemDefinition>	Item registry, keyed by identifier (e.g. minecraft:diamond_sword).
simulateOpenInventory()	void	Silently open the player inventory server-side (no-op if already open).
closeContainer()	void	Close the currently open container.

AbstractInventoryController

itemState.controller. Every mutation goes through here — it produces the correct transaction packets for the current server-auth mode.

Member	Signature	Description
moveItem(from, fromSlot, to, toSlot)	void	Move/merge/swap items between container slots.
dropItem(container, slot, amount)	void	Drop amount items from a slot.
dropItemStack(container, slot)	void	Drop the entire stack in a slot (and swing).
consumeItem(container, slot, amount)	void	Reduce a slot's stack by amount and resync the client.
getLegacyRequestId()	number	Allocate a decreasing legacy transaction request id.
isUsingItem	boolean	Whether the player is currently using/charging an item.
itemInUseDuration	number	Ticks the current item has been in use.

The from/to/container arguments are AbstractInventoryContainers — i.e. localPlayer.inventory, .inventoryArmor, .inventoryOffhand, or a currently open container.

const { entityState, itemState } = ctx.session;
const inv = entityState.localPlayer.inventory;
const armor = entityState.localPlayer.inventoryArmor;

// move whatever is in inventory slot 9 into the helmet slot (slot 0)
itemState.controller.moveItem(inv, 9, armor, 0);

Inventory containers

AbstractInventory                         // content: (ItemStack | undefined)[]
└── AbstractInventoryContainer            // id, type, getSlotType(slot)
    ├── PlayerInventory                   // hotbar + main; hand, selectedSlot, ...
    ├── PlayerInventoryArmor              // helmet/chestplate/leggings/boots
    ├── PlayerInventoryOffhand           // offhand
    └── AbstractDynamicInventory          // opened chests/containers; coordinates, hide()...

AbstractInventory

Member	Type	Description
content	(ItemStack | undefined)[]	Backing slot array. An empty slot is undefined.

Note — there is no isEmpty. A slot is empty exactly when content[slot] === undefined. Check for that rather than looking for an "air" item.

AbstractInventoryContainer (adds)

Member	Signature	Description
id	WindowID	Window id of this container.
type	WindowType	Window type.
getSlotType(slot)	FullContainerName	Container-slot type for a slot index.

PlayerInventory

localPlayer.inventory — the hotbar + main inventory.

Member	Signature	Description
selectedSlot	number	Server-side selected hotbar slot (0–8).
clientSelectedSlot	number	Client-side selected hotbar slot (0–8).
get/set hand	ItemStack | undefined	The item in the held hotbar slot.
setHotbarSlot(slot, toClient?)	void	Switch the held slot (optionally reflect to client).
sendMobEquipment(toClient?)	void	Resend equipment for the current slot.

PlayerInventoryArmor

localPlayer.inventoryArmor — four get/set accessors: helmet, chestplate, leggings, boots (each ItemStack | undefined).

PlayerInventoryOffhand

localPlayer.inventoryOffhand — get offhand (ItemStack | undefined).

AbstractDynamicInventory

An opened container (e.g. a chest). This is the type of itemState.openContainer.

Member	Signature	Description
coordinates	Vector3	World coordinates of the container block, if any.
created	Date	When the container was opened.
get isInitialized	boolean	Whether the container has been initialized.
initialize()	void	Mark it initialized.
get isHidden	boolean	Whether the container is currently hidden (silent).
canHide()	boolean	Whether it can be silent/hidden.
hide()	void	Hide (silence) the container; throws if it can't be.

ItemStack

An immutable item stack. There are no setters — you derive a new stack and reassign it (e.g. to inventory.hand).

Member	Signature	Description
definition	ItemDefinition	The item's static definition.
amount	number	Stack size. (Not count.)
metadata	number	Item metadata/damage value.
block	BlockState | undefined	Associated block state, for placeable items.
nbt	{ version, nbt } | undefined	Raw NBT payload, if any.
get simplifiedNbt	ItemNbt | undefined	Lazily-simplified item NBT.
get nbtHash	number	Hash of the item's NBT (0 if none).
get typeHash	number	Identity hash for grouping "same" items.
get durability	number	Current damage taken (from NBT).
get customColor	Color | undefined	Custom (dyed) color, if set.

Derivations (return a new stack):

Method	Returns	Description
reduceAmount(amount)	ItemStack | undefined	Fewer items (undefined if depleted).
addAmount(amount)	ItemStack	More items.
withAmount(amount)	ItemStack | undefined	Exact amount (undefined if ≤ 0).
withDamage(damage)	ItemStack | undefined	Given damage (undefined if it would break).
withStackId(stackId)	ItemStack	Given network stack id.

Queries:

Method	Returns	Description
canStackWith(other)	boolean	Same type/metadata/nbt as other.
isCorrectTool(block)	boolean	Whether this is the correct tool for block.
newDurability(block)	number	Damage this would take from breaking block.
getDestroySpeed(block)	number	Block-breaking speed against block.

const inv = ctx.session.entityState.localPlayer.inventory;
const held = inv.hand;
if (held) {
  console.log(held.definition.name, "x", held.amount);
}

ItemDefinition

Member	Type	Description
runtimeId	number	Network runtime id.
name	string	Identifier, e.g. minecraft:diamond_sword.
tags	Set<string>	Item tags.
durability	number	Max damage before breaking.
maxStack	number	Max stack size.

Form

itemState.openForm — an open modal form:

Member	Type
form_id	number
data	string (raw JSON)