StartGame

The largest packet of the login: player IDs, spawn position, the full level settings blob (seed, dimension, difficulty, game rules, experiments), block palette, permissions and the movement authority mode.

start-game.bin

struct StartGame {
  ActorUniqueID                                EntityId;
  ActorRuntimeID                               RuntimeId;
  GameType                                     EntityGameType;
  Vec3                                         Pos;
  Vec2                                         Rot;
  LevelSettings                                Settings;
  string                                       LevelId;
  string                                       LevelName;
  string                                       TemplateContentIdentity;
  bool                                         IsTrial;
  SyncedPlayerMovementSettings                 MovementSettings;
  uint64 (LE)                                  LevelCurrentTime;
  varint32                                     EnchantmentSeed;
  varuint32 [] · ServerBlockProperty[]         BlockProperties;
  string                                       MultiplayerCorrelationId;
  bool                                         EnableItemStackNetManager;
  string                                       ServerVersion;
  CompoundTag                                  PlayerPropertyData;
  uint64 (LE)                                  ServerBlockTypeRegistryChecksum;
  uuid.UUID                                    WorldTemplateId;
  bool                                         ServerEnabledClientSideGeneration;
  bool                                         BlockNetworkIdsAreHashes;
  NetworkPermissions                           NetworkPermissions;
  optional byte + ServerConfigurationJoinInfo  ServerConfigurationJoinInfo;
  ServerTelemetryData                          ServerTelemetryData;
}

Structure

Field	Type	Description
Entity Id	ActorUniqueID
Runtime Id	ActorRuntimeID
Entity Game Type	GameType
Pos	Vec3
Rot	Vec2
Settings	LevelSettings
Level Id	string
Level Name	string
Template Content Identity	string
Is Trial	bool
Movement Settings	SyncedPlayerMovementSettings
Level Current Time	uint64 (LE)
Enchantment Seed	varint32
Block Properties	varuint32 count + ServerBlockProperty[]	Length-prefixed sequence.
Multiplayer Correlation Id	string
Enable Item Stack Net Manager	bool
Server Version	string
Player Property Data	CompoundTag
Server Block Type Registry Checksum	uint64 (LE)
World Template Id	uuid.UUID
Server Enabled Client Side Generation	bool
Block Network Ids Are Hashes	bool
Network Permissions	NetworkPermissions
Server Configuration Join Info	optional byte + ServerConfigurationJoinInfo	Presence flag on the wire; value omitted when absent.
Server Telemetry Data	ServerTelemetryData

Structure of Vec3

Field	Type	Description
X	float32 (LE)
Y	float32 (LE)
Z	float32 (LE)

Structure of Vec2

Field	Type	Description
X	float32 (LE)
Y	float32 (LE)

Structure of LevelSettings

Field	Type	Description
Seed	uint64 (LE)
Spawn Settings	SpawnSettings
Generator	GeneratorType
Game Type	GameType
Is Hardcore	bool
Game Difficulty	Difficulty
Default Spawn	BlockPos
Achievements Disabled	bool
Editor World Type	WorldType
Is Created In Editor	bool
Is Exported From Editor	bool
Time	varint32
Education Edition Offer	EducationEditionOffer
Education Features Enabled	bool
Education Product Id	string
Rain Level	float32 (LE)
Lightning Level	float32 (LE)
Confirmed Platform Locked Content	bool
Multiplayer Game Intent	bool
Lan Broadcast Intent	bool
Xbl Broadcast Intent	GamePublishSetting
Platform Broadcast Intent	GamePublishSetting
Commands Enabled	bool
Texture Packs Required	bool
Rule Data	GameRulesChangedPacketData
Experiments	Experiments
Bonus Chest Enabled	bool
Start With Map Enabled	bool
Default Permissions	PlayerPermissionLevel
Server Chunk Tick Range	int32 (LE)
Has Locked Behavior Pack	bool
Has Locked Resource Pack	bool
Is From Locked Template	bool
Use Msa Gamertags Only	bool
Is From World Template	bool
Is World Template Option Locked	bool
Spawn V1 Villagers	bool
Persona Disabled	bool
Custom Skins Disabled	bool
Emote Chat Muted	bool
Base Game Version	string
Limited World Width	int32 (LE)
Limited World Depth	int32 (LE)
Nether Type	NetherWorldType
Edu Shared Uri Resource	EduSharedUriResource
Override Force Experimental Gameplay	optional byte + bool	Presence flag on the wire; value omitted when absent.
Chat Restriction Level	ChatRestrictionLevel
Disable Player Interactions	bool
Server Editor Connection Policy	ServerEditorConnectionPolicy
Allow Anonymous Block Drops In Editor Worlds	bool

Structure of SyncedPlayerMovementSettings

Field	Type	Description
Rewind History Size	varint32
Server Auth Block Breaking	bool

Structure of ServerBlockProperty

Field	Type	Description
Name	string
Tag	CompoundTag

Structure of NetworkPermissions

Field	Type	Description
Server Auth Sound Enabled	bool

Structure of ServerConfigurationJoinInfo

Field	Type	Description
Gatherings Configuration	optional byte + GatheringsConfigurationJoinInfo	Presence flag on the wire; value omitted when absent.
Client Store Entry Point Configuration	optional byte + ClientStoreEntryPointConfiguration	Presence flag on the wire; value omitted when absent.
Presence Configuration	optional byte + PresenceConfiguration	Presence flag on the wire; value omitted when absent.

Structure of ServerTelemetryData

Field	Type	Description
Server Id	string
Scenario Id	string
World Id	string
Owner Id	string

Structure of SpawnSettings

Field	Type	Description
Type	int16 (LE)
User Defined Biome Name	string
Dimension	DimensionType

Structure of BlockPos

Field	Type	Description
X	varint32
Y	varint32
Z	varint32

Structure of GameRulesChangedPacketData

Field	Type	Description
Rules	varuint32 count + GameRule[]	Length-prefixed sequence.

Structure of Experiments

Field	Type	Description
Toggles	uint32 count + ExperimentToggle[]	Length-prefixed sequence.
Experiments Ever Toggled	bool

Structure of EduSharedUriResource

Field	Type	Description
Button Name	string
Link Uri	string

Notes

Sent after ResourcePackStackFinished, together with DimensionData, JigsawStructureData, VoxelShapes and ItemRegistry.
LevelSettings is a big nested struct: world seed, spawn position, difficulty, game rules, io reader settings, experiments, server auth movement mode and more.
Runtime IDs issued here are used by every later actor packet.
Spawn completes when the client answers RequestChunkRadius → ChunkRadiusUpdated → PlayStatus(PlayerSpawn) → SetLocalPlayerAsInitialised.