Guide
Reference
Architecture
Contributing
Performance
Guide
Reference
Architecture
Contributing
Performance

Entity Metadata

The Set Entity Data packet (clientbound; see ./entities) carries an entity's synced data fields — a sparse map of typed values keyed by an unsigned-byte index. Every entity class declares its set of fields with a stable index assignment that subclasses extend.

Wire layout

Set Entity Data is:

VarInt entity_id
loop:
  UByte index
  if index == 0xFF: break
  VarInt serializer_type_id
  <value>            (length and shape determined by serializer_type_id)

The 0xFF byte is the terminator marker. A packet with no fields therefore has body [VarInt entity_id, 0xFF].

serializer_type_id is an index into the global EntityDataSerializers registry (a numeric ID, registered in fixed order by the client; see the table below).

Serializer types

The order below matches the registration order in vanilla and therefore the wire IDs.

ID Name Encoding
0 Byte 1 byte.
1 VarInt VarInt.
2 Long VarLong.
3 Float 4 bytes IEEE 754.
4 String VarInt length + UTF-8 bytes.
5 Component "Trusted" text component (network NBT).
6 Optional Component Boolean present; if true, Component.
7 Slot / ItemStack See ./slot.
8 Boolean 1 byte (0 / 1).
9 Rotations 3 × Float (pitch, yaw, roll, in degrees).
10 BlockPos Long (packed 26-bit X / 12-bit Y / 26-bit Z).
11 Optional BlockPos Boolean present; if true, BlockPos.
12 Direction VarInt enum (0=down, 1=up, 2=north, 3=south, 4=west, 5=east).
13 Optional living entity reference Boolean present; if true, UUID of the referenced living entity.
14 Block State VarInt — block-state registry ID.
15 Optional Block State VarInt; 0 means absent, otherwise id (encoded as id + 0; vanilla uses 0 as sentinel for "no state").
16 Particle Particle ID (VarInt) + type-specific options (see ./particle).
17 Particles VarInt count + repeated Particle.
18 Villager Data VarInt type + VarInt profession + VarInt level.
19 Optional Unsigned Int VarInt; 0 means absent, otherwise value + 1.
20 Pose VarInt enum (0=standing, 1=fall_flying, 2=sleeping, 3=swimming, 4=spin_attack, 5=crouching, 6=long_jumping, 7=dying, 8=croaking, 9=using_tongue, 10=sitting, 11=roaring, 12=sniffing, 13=emerging, 14=digging, 15=sliding, 16=shooting, 17=inhaling — exact values follow the Pose enum order).
21 Cat Variant VarInt — registry holder ID into minecraft:cat_variant.
22 Cat Sound Variant VarInt — registry holder ID.
23 Cow Variant VarInt — registry holder ID.
24 Cow Sound Variant VarInt — registry holder ID.
25 Wolf Variant VarInt — registry holder ID.
26 Wolf Sound Variant VarInt — registry holder ID.
27 Frog Variant VarInt — registry holder ID.
28 Pig Variant VarInt — registry holder ID.
29 Pig Sound Variant VarInt — registry holder ID.
30 Chicken Variant VarInt — registry holder ID.
31 Chicken Sound Variant VarInt — registry holder ID.
32 Zombie Nautilus Variant VarInt — registry holder ID.
33 Optional Global Position Boolean present; if true, dimension Identifier + BlockPos.
34 Painting Variant VarInt — registry holder ID into minecraft:painting_variant.
35 Sniffer State VarInt enum (0=idling, 1=feeling_happy, 2=scenting, 3=sniffing, 4=searching, 5=digging, 6=rising).
36 Armadillo State VarInt enum (0=idle, 1=rolling, 2=scared, 3=unrolling).
37 Copper Golem State VarInt enum.
38 Weathering Copper State VarInt enum (0=unaffected, 1=exposed, 2=weathered, 3=oxidized).
39 Vector3 3 × Float.
40 Quaternion 4 × Float (x, y, z, w).
41 Resolvable Profile Optional name + UUID + property set (see profile encoding).
42 Humanoid Arm VarInt enum (0=left, 1=right).

NOTE: A serializer type (and its wire ID) can shift between vanilla snapshots when new types are added. The IDs above match the registration order in 26.1.2's EntityDataSerializers.

The "registry holder" types (variants, sound variants, painting variants) use the standard holder encoding: a positive VarInt is id + 1 referring to the dynamic registry entry, and 0 means an inline payload follows (rare for variants; primarily used for sound events).

Indexed schema by class

The index byte assignment is hierarchical. Each subclass appends indices starting after its parent's last assigned index. The full chain for a typical mob is Entity → LivingEntity → Mob → AgeableMob → Animal → <species>.

Entity (base — indices 0..7)

Index Type Field
0 Byte (flags) Bitset: 0x01 on fire, 0x02 sneaking, 0x04 unused, 0x08 sprinting, 0x10 swimming, 0x20 invisible, 0x40 glowing, 0x80 elytra-flying.
1 VarInt Air ticks (default 300).
2 Optional Component Custom name.
3 Boolean Custom name visible.
4 Boolean Silent.
5 Boolean No gravity.
6 Pose Current pose.
7 VarInt Frozen ticks (powder snow).

LivingEntity (extends Entity — indices 8..14)

Index Type Field
8 Byte (flags) 0x01 hand active, 0x02 offhand, 0x04 in spin attack.
9 Float Health.
10 VarInt Potion effect particle color (packed ARGB or 0 if none).
11 Boolean Potion effect particles ambient.
12 VarInt Number of arrows stuck.
13 VarInt Number of bee stingers.
14 Optional BlockPos Sleeping position.

Mob (extends LivingEntity — index 15)

Index Type Field
15 Byte (flags) 0x01 no AI, 0x02 left-handed, 0x04 aggressive.

Player (extends LivingEntity — indices 15..20)

Index Type Field
15 Float Additional hearts (absorption).
16 VarInt Score (used in death screen).
17 Byte Skin part bitmask: 0x01 cape, 0x02 jacket, 0x04 left sleeve, 0x08 right sleeve, 0x10 left pants, 0x20 right pants, 0x40 hat.
18 Byte Main hand (0=left, 1=right).
19 NBT compound Left shoulder entity (parrot).
20 NBT compound Right shoulder entity (parrot).

Common species extensions

Each entity class defines its own additional indices on top of Mob. For example:

  • Wolf adds: tame flags byte, owner UUID (optional), collar color VarInt, variant holder, sound variant holder.
  • Cat adds: variant holder, sound variant holder, lying-down boolean, relaxed-meow boolean, collar color.
  • Painting (extends Entity, not Mob): variant holder at the next free index after Entity.
  • Display family (item_display, block_display, text_display): a large block of transformation fields (interpolation start, duration, scale, translation, rotation, billboard mode, brightness, view range, shadow radius, shadow strength, width, height, glow color override, plus type-specific fields).

The authoritative per-class index tables live in each subclass's static initializer in the vanilla source (see the defineId(...) calls in classes under net.minecraft.world.entity.*).

Source: net/minecraft/network/syncher/EntityDataSerializers.java, net/minecraft/network/syncher/SynchedEntityData.java, net/minecraft/network/protocol/game/ClientboundSetEntityDataPacket.java, net/minecraft/world/entity/Entity.java, net/minecraft/world/entity/LivingEntity.java, net/minecraft/world/entity/Mob.java, net/minecraft/world/entity/player/Player.java, net/minecraft/world/entity/Pose.java.

ON THIS PAGE