Slot Data

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The slot data structure is how Minecraft represents an item and its associated data in the minecraft protocol


The structure consists of at least a short, which gives the item/block ID [1]. A value of -1 signifies that the slot is empty, and no further data follows.

If the block ID is not -1, three more fields follow. These fields are a byte (item count), a short (item damage), and another short (length of optional NBT data).

If the short (length of NBT data) is -1, there is no NBT data, and no further data follows. Otherwise, a byte array will follow.

The byte array contains gzipped (that is RFC 1952 rather than RFC 1950) NBT data. The format of this data is as follows:

   LIST: 'ench'
       SHORT: 'id'
       SHORT: 'lvl'

Each of the inner, untagged COMPOUNDs represents an enchantment, with its ID[2] and level given as child SHORT elements.


 ff ff                            | empty slot
 01 16 01 00 00 ff ff             | a diamond pickaxe
 01 16 01 00 00 00 04 CA FE BA BE | a diamond pickaxe with (made-up) NBT data