Pre-release protocol

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This page documents the changes from the last stable Minecraft release (currently 1.19.4, protocol 762) to the current pre-release (currently 23w18a, protocol Snapshot 133). Note that this page contains bleeding-edge information that may not be completely or correctly documented.

One who wishes to commandeer the merging of this into Protocol when an update is made must be sure to respect any changes that may have occurred to the respective packets there.

Contents

Data types

No changes so far.

Packets

ID Packet name Documentation
Play clientbound
0x24 Chunk Data and Update Light Current Pre
0x27 Update Light Current Pre
0x31 Open Sign Editor Current Pre
0x43 Update Section Blocks Current Pre
0x69 Update Advancements Current Pre
0x6B Feature Flags Current Pre
0x6D Update Recipes Current Pre
Play serverbound
0x2E Update Sign Current Pre

New/modified data types

No changes so far.

Entity Metadata

No changes so far.

Entity

No changes so far.

Block Actions

No changes so far.

Inventories

Type Name Description
0 minecraft:generic_9x1 A 1-row inventory, not used by the notchian server.
1 minecraft:generic_9x2 A 2-row inventory, not used by the notchian server.
2 minecraft:generic_9x3 General-purpose 3-row inventory. Used by Chest, minecart with chest, ender chest, and barrel
3 minecraft:generic_9x4 A 4-row inventory, not used by the notchian server.
4 minecraft:generic_9x5 A 5-row inventory, not used by the notchian server.
5 minecraft:generic_9x6 General-purpose 6-row inventory, used by large chests.
6 minecraft:generic_3x3 General-purpose 3-by-3 square inventory, used by Dispenser and Dropper
7 minecraft:anvil Anvil
8 minecraft:beacon Beacon
9 minecraft:blast_furnace Blast Furnace
10 minecraft:brewing_stand Brewing stand
11 minecraft:crafting Crafting table
12 minecraft:enchantment Enchantment table
13 minecraft:furnace Furnace
14 minecraft:grindstone Grindstone
15 minecraft:hopper Hopper or minecart with hopper
16 minecraft:lectern Lectern
17 minecraft:loom Loom
18 minecraft:merchant Villager, Wandering Trader
19 minecraft:shulker_box Shulker box
20 minecraft:legacy_smithing Smithing Table

Warning.png The Notchian server only sends this type if feature flag update_1_20 was not enabled

21 20 minecraft:smithing Smithing Table

Warning.png The Notchian server only sends this type if feature flag update_1_20 was enabled

22 21 minecraft:smoker Smoker
23 22 minecraft:cartography Cartography Table
24 23 minecraft:stonecutter Stonecutter

Plugin Channels

No changes so far.

Play

Clientbound

Chunk Data and Update Light

Main article: Chunk Format
See also: #Unload Chunk
Huh.png The following information needs to be added to this page:
How do biomes work now? The biome change happened at the same time as the seed change, but it's not clear how/if biomes could be computed given that it's not the actual seed... (/r/mojira discussion which notes that it seems to be some kind of interpolation)

This packet sends all block entities in the chunk (though sending them is not required; it is still legal to send them with Block Entity Data later). The light data in this packet is the same format as in the Update Light packet.

Packet ID State Bound To Field Name Field Type Notes
0x24 Play Client Chunk X Int Chunk coordinate (block coordinate divided by 16, rounded down)
Chunk Z Int Chunk coordinate (block coordinate divided by 16, rounded down)
Heightmaps NBT Compound containing one long array named MOTION_BLOCKING, which is a heightmap for the highest solid block at each position in the chunk (as a compacted long array with 256 entries, with the number of bits per entry varying depending on the world's height, defined by the formula ceil(log2(height + 1))). The Notchian server also adds a WORLD_SURFACE long array, the purpose of which is unknown, but it's not required for the chunk to be accepted.
Size VarInt Size of Data in bytes
Data Byte array See data structure in Chunk Format
Number of block entities VarInt Number of elements in the following array
Block Entity Packed XZ Array Byte The packed section coordinates, calculated from ((blockX & 15) << 4) | (blockZ & 15)
Y Short The height relative to the world
Type VarInt The type of block entity
Data NBT The block entity's data, without the X, Y, and Z values
Trust Edges Boolean If edges should be trusted for light updates.
Sky Light Mask BitSet BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has data in the Sky Light array below. The least significant bit is for blocks 16 blocks to 1 block below the min world height (one section below the world), while the most significant bit covers blocks 1 to 16 blocks above the max world height (one section above the world).
Block Light Mask BitSet BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has data in the Block Light array below. The order of bits is the same as in Sky Light Mask.
Empty Sky Light Mask BitSet BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has all zeros for its Sky Light data. The order of bits is the same as in Sky Light Mask.
Empty Block Light Mask BitSet BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has all zeros for its Block Light data. The order of bits is the same as in Sky Light Mask.
Sky Light array count VarInt Number of entries in the following array; should match the number of bits set in Sky Light Mask
Sky Light arrays Length Array VarInt Length of the following array in bytes (always 2048)
Sky Light array Array of 2048 bytes There is 1 array for each bit set to true in the sky light mask, starting with the lowest value. Half a byte per light value. Indexed ((y<<8) | (z<<4) | x) / 2 If there's a remainder, masked 0xF0 else 0x0F.
Block Light array count VarInt Number of entries in the following array; should match the number of bits set in Block Light Mask
Block Light arrays Length Array VarInt Length of the following array in bytes (always 2048)
Block Light array Array of 2048 bytes There is 1 array for each bit set to true in the block light mask, starting with the lowest value. Half a byte per light value. Indexed ((y<<8) | (z<<4) | x) / 2 If there's a remainder, masked 0xF0 else 0x0F.

Note that the Notchian client requires an Set Center Chunk packet when it crosses a chunk border, otherwise it'll only display render distance + 2 chunks around the chunk it spawned in.

The compacted array format has been adjusted so that individual entries no longer span across multiple longs, affecting the main data array and heightmaps.

New format, 5 bits per block, containing the following references to blocks in a palette (not shown): 122344566480743131516914101202

0020863148418841 0000000000100000100001100011000101001000010000011000100001000001
01018A7260F68C87 0000000100000001100010100111001001100000111101101000110010000111

Update Light

Updates light levels for a chunk. See Light for information on how lighting works in Minecraft.

Packet ID State Bound To Field Name Field Type Notes
0x27 Play Client Chunk X VarInt Chunk coordinate (block coordinate divided by 16, rounded down)
Chunk Z VarInt Chunk coordinate (block coordinate divided by 16, rounded down)
Trust Edges Boolean If edges should be trusted for light updates.
Sky Light Mask BitSet BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has data in the Sky Light array below. The least significant bit is for blocks 16 blocks to 1 block below the min world height (one section below the world), while the most significant bit covers blocks 1 to 16 blocks above the max world height (one section above the world).
Block Light Mask BitSet BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has data in the Block Light array below. The order of bits is the same as in Sky Light Mask.
Empty Sky Light Mask BitSet BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has all zeros for its Sky Light data. The order of bits is the same as in Sky Light Mask.
Empty Block Light Mask BitSet BitSet containing bits for each section in the world + 2. Each set bit indicates that the corresponding 16×16×16 chunk section has all zeros for its Block Light data. The order of bits is the same as in Sky Light Mask.
Sky Light array count VarInt Number of entries in the following array; should match the number of bits set in Sky Light Mask
Sky Light arrays Length Array VarInt Length of the following array in bytes (always 2048)
Sky Light array Array of 2048 bytes There is 1 array for each bit set to true in the sky light mask, starting with the lowest value. Half a byte per light value.
Block Light array count VarInt Number of entries in the following array; should match the number of bits set in Block Light Mask
Block Light arrays Length Array VarInt Length of the following array in bytes (always 2048)
Block Light array Array of 2048 bytes There is 1 array for each bit set to true in the block light mask, starting with the lowest value. Half a byte per light value.

A bit will never be set in both the block light mask and the empty block light mask, though it may be present in neither of them (if the block light does not need to be updated for the corresponding chunk section). The same applies to the sky light mask and the empty sky light mask.

Open Sign Editor

Sent when the client has placed a sign and is allowed to send Update Sign. There must already be a sign at the given location (which the client does not do automatically) - send a Block Update first.

Packet ID State Bound To Field Name Field Type Notes
0x31 Play Client Location Position
Is Front Text Boolean Whether the opened editor is for the front or on the back of the sign

Update Section Blocks

Fired whenever 2 or more blocks are changed within the same chunk on the same tick.

Warning.png Changing blocks in chunks not loaded by the client is unsafe (see note on Block Update).

Packet ID State Bound To Field Name Field Type Notes
0x43 Play Client Chunk section position Long Chunk section coordinate (encoded chunk x and z with each 22 bits, and section y with 20 bits, from left to right).
Suppress Light Updates Boolean Whether to ignore light updates caused by the contained changes. Always inverse the preceding Update Light packet's "Trust Edges" bool
Blocks array size VarInt Number of elements in the following array.
Blocks Array of VarLong Each entry is composed of the block state id, shifted left by 12, and the relative block position in the chunk section (4 bits for x, z, and y, from left to right).

Chunk section position is encoded:

((sectionX & 0x3FFFFF) << 42) | (sectionY & 0xFFFFF) | ((sectionZ & 0x3FFFFF) << 20);

and decoded:

sectionX = long >> 42;
sectionY = long << 44 >> 44;
sectionZ = long << 22 >> 42;

Blocks are encoded:

blockStateId << 12 | (blockLocalX << 8 | blockLocalZ << 4 | blockLocalY)
//Uses the local position of the given block position relative to its respective chunk section

Update Advancements

Packet ID State Bound To Field Name Field Type Notes
0x69 Play Client Reset/Clear Boolean Whether to reset/clear the current advancements.
Mapping size VarInt Size of the following array.
Advancement mapping Key Array Identifier The identifier of the advancement.
Value Advancement See below
List size VarInt Size of the following array.
Identifiers Array of Identifier The identifiers of the advancements that should be removed.
Progress size VarInt Size of the following array.
Progress mapping Key Array Identifier The identifier of the advancement.
Value Advancement progress See below.

Advancement structure:

Field Name Field Type Notes
Has parent Boolean Indicates whether the next field exists.
Parent id Optional Identifier The identifier of the parent advancement.
Has display Boolean Indicates whether the next field exists.
Display data Optional advancement display See below.
Number of criteria VarInt Size of the following array.
Criteria Key Array Identifier The identifier of the criterion.
Value Void There is no content written here. Perhaps this will be expanded in the future?
Array length VarInt Number of arrays in the following array.
Requirements Array length 2 Array VarInt Number of elements in the following array.
Requirement Array of String Array of required criteria.
Sends telemetry data Boolean Whether the client should include this achievement in the telemetry data when it's completed.

The Notchian client only sends data for advancements on the minecraft namespace.

Advancement display:

Field Name Field Type Notes
Title Chat
Description Chat
Icon Slot
Frame type VarInt Enum 0 = task, 1 = challenge, 2 = goal.
Flags Int 0x01: has background texture; 0x02: show_toast; 0x04: hidden.
Background texture Optional Identifier Background texture location. Only if flags indicates it.
X coord Float
Y coord Float

Advancement progress:

Field Name Field Type Notes
Size VarInt Size of the following array.
Criteria Criterion identifier Array Identifier The identifier of the criterion.
Criterion progress Criterion progress

Criterion progress:

Field Name Field Type Notes
Achieved Boolean If true, next field is present.
Date of achieving Optional Long As returned by Date.getTime.

Feature Flags

Used to enable and disable features, generally experimental ones, on the client.

Packet ID State Bound To Field Name Field Type Notes
0x6B Play Client Total Features VarInt Number of features that appear in the array below.
Feature Flags Identifier Array

As of 1.19.4 1.20, the following feature flags are available:

  • minecraft:vanilla - enables vanilla features
  • minecraft:bundle - enables support for the bundle
  • minecraft:update_1_20 - enables all the Minecraft 1.20 features that are available in 1.19.4

Update Recipes

Packet ID State Bound To Field Name Field Type Notes
0x6D Play Client Num Recipes VarInt Number of elements in the following array.
Recipe Type Array Identifier The recipe type, see below.
Recipe ID Identifier
Data Varies Additional data for the recipe.

Recipe types:

Type Description Data
minecraft:crafting_shapeless Shapeless crafting recipe. All items in the ingredient list must be present, but in any order/slot. As follows:
Name Type Description
Group String Used to group similar recipes together in the recipe book. Tag is present in recipe JSON.
Category VarInt Enum Building = 0, Redstone = 1, Equipment = 2, Misc = 3
Ingredient count VarInt Number of elements in the following array.
Ingredients Array of Ingredient.
Result Slot
minecraft:crafting_shaped Shaped crafting recipe. All items must be present in the same pattern (which may be flipped horizontally or translated). As follows:
Name Type Description
Width VarInt
Height VarInt
Group String Used to group similar recipes together in the recipe book. Tag is present in recipe JSON.
Category VarInt Enum Building = 0, Redstone = 1, Equipment = 2, Misc = 3
Ingredients Array of Ingredient Length is width * height. Indexed by x + (y * width).
Result Slot
Show notification Boolean Show a toast when the recipe is added.
minecraft:crafting_special_armordye Recipe for dying leather armor As follows:
Name Type Description
Category VarInt Enum Building = 0, Redstone = 1, Equipment = 2, Misc = 3
minecraft:crafting_special_bookcloning Recipe for copying contents of written books
minecraft:crafting_special_mapcloning Recipe for copying maps
minecraft:crafting_special_mapextending Recipe for adding paper to maps
minecraft:crafting_special_firework_rocket Recipe for making firework rockets
minecraft:crafting_special_firework_star Recipe for making firework stars
minecraft:crafting_special_firework_star_fade Recipe for making firework stars fade between multiple colors
minecraft:crafting_special_repairitem Recipe for repairing items via crafting
minecraft:crafting_special_tippedarrow Recipe for crafting tipped arrows
minecraft:crafting_special_bannerduplicate Recipe for copying banner patterns
minecraft:crafting_special_shielddecoration Recipe for applying a banner's pattern to a shield
minecraft:crafting_special_shulkerboxcoloring Recipe for recoloring a shulker box
minecraft:crafting_special_suspiciousstew Recipe for crafting suspicious stews
minecraft:crafting_decorated_pot Recipe for crafting decorated pots

Warning.png The Notchian server only sends this recipe if feature flag update_1_20 was enabled

minecraft:smelting Smelting recipe As follows:
Name Type Description
Group String Used to group similar recipes together in the recipe book.
Category VarInt Enum Food = 0, Blocks = 1, Misc = 2
Ingredient Ingredient
Result Slot
Experience Float
Cooking time VarInt
minecraft:blasting Blast furnace recipe
minecraft:smoking Smoker recipe
minecraft:campfire_cooking Campfire recipe
minecraft:stonecutting Stonecutter recipe As follows:
Name Type Description
Group String Used to group similar recipes together in the recipe book. Tag is present in recipe JSON.
Ingredient Ingredient
Result Slot
minecraft:smithing Smithing table recipe

Warning.png The Notchian server only sends this recipe if feature flag update_1_20 was not enabled

As follows:
Name Type Description
Base Ingredient First item.
Addition Ingredient Second item.
Result Slot
minecraft:smithing_transform Recipe for smithing netherite gear

Warning.png The Notchian server only sends this recipe if feature flag update_1_20 was enabled. It supersedes the minecraft:smithing recipe type

As follows:
Name Type Description
Template Ingredient The smithing template.
Base Ingredient The base item.
Addition Ingredient The additional ingredient.
Result Slot
minecraft:smithing_trim Recipe for applying armor trims

Warning.png The Notchian server only sends this recipe if feature flag update_1_20 was enabled. It supersedes the minecraft:smithing recipe type

As follows:
Name Type Description
Template Ingredient The smithing template.
Base Ingredient The base item.
Addition Ingredient The additional ingredient.

Ingredient is defined as:

Name Type Description
Count VarInt Number of elements in the following array.
Items Array of Slot Any item in this array may be used for the recipe. The count of each item should be 1.

Serverbound

Update Sign

This message is sent from the client to the server when the “Done” button is pushed after placing a sign.

The server only accepts this packet after Open Sign Editor, otherwise this packet is silently ignored.

Packet ID State Bound To Field Name Field Type Notes
0x2E Play Server Location Position Block Coordinates.
Is Front Text Boolean Whether the updated text is in front or on the back of the sign
Line 1 String (384) First line of text in the sign.
Line 2 String (384) Second line of text in the sign.
Line 3 String (384) Third line of text in the sign.
Line 4 String (384) Fourth line of text in the sign.

Status

Clientbound

No changes so far.

Serverbound

No changes so far.

Login

Clientbound

No changes so far.

Serverbound

No changes so far.