Object Data

This article documents the Data field in the Spawn Object packet. The field is of type Int, and the meaning of its contents depend on the type of object being spawned, as defined in the Type field of the same packet, and is documented below.

In some cases, the data field has no meaning, but is only used to indicate presence of velocity. In others, it (and velocity) is always ignored.

Item (id 2)
The int value is ignored, but should be set to  to indicate that velocity is present.

Minecarts (id 10)
The int value itself specifies the minecart's functionality:

Item Frame (id 71)
You have to set both Orientation and Yaw/Pitch accordingly, otherwise it will not work.

Velocity in the packet is always ignored.

Falling Block (id 70)
Velocity in the packet is always ignored.

Fishing Float (id 90)
Velocity in the packet is ignored, and instead should be inferred from the shooter's position.

Llama spit (id 68)
Velocity is always used even though the data field is always 0.

Fireball (id 63), small fireball (id 64), dragon fireball (id 93), and wither skull (id 66)
The data field stores the ID of the shooting entity, or 0 if there was no shooting entity. Velocity is used even if data is set to 0.

Shulker bullet (id 67)
Velocity is always used even though the data field is always 0.

Potion (id 73)
Velocity in the packet is always ignored.

EXP bottle (id 75)
Velocity in the packet is always ignored.