Protocol 26.1.2 — Overview#

This section specifies the Minecraft Java Edition network protocol as shipped with Minecraft 26.1.2 (mcVersion=26.1.2 in PaperMC). Mojang dropped the 1.x.y versioning scheme; the version this spec targets is simply 26.1.2. It describes the wire format, every packet of every state, and the subsystems a server must implement to serve a vanilla client.

How to read this section#

Start with the foundations, then move to the state-by-state packet listings, and finally the cross-cutting subsystems.

1. Foundations
   • Data Types — primitive encodings (VarInt, NBT, Position…) used everywhere below.
   • Text Component — the rich-text format used in chat, titles, item names.
   • Slot / ItemStack — items on the wire, including data components.
   • Particle — particle descriptors used in level events.
   • Connection Lifecycle — state machine and packet ordering.
2. States (in chronological order of the connection)
   • Handshake
   • Status
   • Login
   • Configuration
   • Play — Clientbound
   • Play — Serverbound
3. Subsystems
   • Registries
   • Tags
   • Chunks & Lighting
   • Entities
   • Entity Metadata
   • Commands
   • Chat System

Framing#

Every packet on the wire is framed as:

• Length is the total length, in bytes, of Packet ID + Payload. It does not include itself.
• Packet ID identifies the packet within the current state and direction.
• Payload is the packet's body, encoded according to the field list in the relevant state page.

Once the connection enters the compression mode (see Login), the framing changes:

• If Data Length is 0, the rest of the packet is uncompressed.
• Otherwise, Data Length is the uncompressed size, and the remainder is zlib-compressed.

Encryption, when enabled, is applied as an outer AES/CFB8 layer over the framed bytes.