Protocol FAQ

People very, very often have questions regarding the Minecraft Beta Protocol, so we'll try to address some of the most common ones on this document. If you're still having trouble, join us on IRC, channel #mcdevs on irc.freenode.net.

Is the protocol documentation complete?

Depending on your definition, yes! All packet types are known and their layout documented. Some finer details are missing, but everything you need to make functional programs is present. We have a script that monitors for new versions of the client and notifies us, allowing us to quickly document new packets.

What's the normal login sequence for a client?

See Authentication for communication with minecraft.net

The recommended login sequence looks like this, where C is the client and S is the server:

C ↔ S : Connects
C → S : Sends handshake
C ← S : Sends handshake response
C → S : After authenticating (if needed), sends the login packet
C ← S : Either kicks (invalid login) or sends a login response
C ← S : Sends pre-chunks and chunks and entities
C ← S : Sends spawn position
C ← S : Sends inventory [Need to verify this since inventory changed] (beta 1.1_02: looks like Window items with type=0, then a Set slot with window id = -1 and slot = -1)
C ← S : Tell the client they're ready to spawn by sending a position + look packet. Note: The stance and Y should be swapped when the server sends it to the client (See Protocol Page)!
C → S : Sends a position + look packet to confirm the spawn position, with the stance and Y swapped back to the correct positions

I think I've done everything right, but…

…my player isn't spawning!

After sending the common-sense packets (Handshake, Login, Inventory, Compass and Pre-chunk/Chunk pairs) you need to finally send the player their initial position for them to leave the "Loading Map" screen.

…my client isn't receiving complete map chunks!

Main article: How to Write a Client

The standard Minecraft server server sends full chunks only when your client is sending player status update packets (any of Player (0x0A) through Player Position & Look (0x0D)).

…all connecting clients spasm and jerk uncontrollably!

For newer clients, your server needs to send 49 chunks ahead of time, not just one. Send a 7x7 square of chunks, centered on the connecting client's position, before spawning them.