Minecraft:Java Edition 1.21.5 Pre-Release 1

1.21.5 Pre-Release 1 (known as 1.21.5-pre1 in the Minecraft:launcher) is the first pre-release for Minecraft:Java Edition 1.21.5, released on March 11, 2025.<ref>Template:Mcnet</ref> This is the first pre-release released in 2025.

Changes

Items

Minecraft:Spawn eggs

• Added textures for Minecraft:Programmer Art resource pack.

World generation

Minecraft:Fallen trees

• The longer versions of fallen birch trees now generate properly.
  • This version is up to 15 blocks long, as opposed to the shorter version which can only reach 8 blocks at most.

Command format

General

• Arguments in commands that accept inline values like loot tables, predicates, modifiers, data components, formatted text (Template:Cmd, Template:Cmd, Template:Cmd, Template:Cmd, data components in Template:Cmd, etc.) have been reverted to accept numbers in place of booleans.

General

Network protocol

• The client-bound Template:Cd packet now contains an index increasing for every message sent to the client.
  • The index starts at 0 when logging in (or is reset by configuration phase and the Template:Cd packet).
  • For every message, the server should increment this value by 1.
  • If this value updates in an unexpected way, the client will disconnect.
  • As the protocol requires that every chat packet reaches the client in produced order, the goal is to enable faster detection of missed/reordered chat messages for custom server developers.
• The server-bound Template:Cd and Template:Cd packets now contain a checksum byte along with the 'last seen' update.
  • This is a simple hash of the 'last seen' signatures which should be reconstructed by the server, allowing quicker detection of desynchronized state.
  • This can be passed as Template:Cd to disable the check, for compatibility with protocol translation.

Minecraft:Resource pack

• The version is now Template:Cd.
• Tweaked Minecraft:leaf litter block models.