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Documentation on the server protocol used by the Minecraft Classic Creative server.

Minecraft.net Communication[]


To be able to connect to a server in Minecraft Classic from the Server List, a server must broadcast to minecraft.net a so-called "heartbeat" every few minutes[to check: some experiments with a python server show that is not more used].

The stock server broadcasts this heartbeat every 45 seconds.

A "heartbeat" takes the form of an HTTP request to https://minecraft.net/heartbeat.jsp. After sending a heartbeat, the URL for the server is returned.

It is critical to a successful heartbeat that you leave out the "www" in the HTTP request, as you are going to be targeting it as a URI, not a URL.

It can be a GET or POST request. A table of the required parameters is below:

Name Details
port Port number of the server. This is usually 25565
max Maximum number of players on the server
name The name of the server
public Whether the server is public (i.e. appears in the server list) or not. Can be True or False, in that capitalization.
version Protocol version number, this should be 7 unless you're using a client version older than 0.28.
salt A random, 16-character base-62 salt
users Number of users connected to the server

The simplest way to send a heartbeat is to open a TCP socket to port 80 on minecraft.net, and send the following (with the values changed, obviously):

GET /heartbeat.jsp?port=25565&max=32&name=My%20Server&public=True&version=7&salt=wo6kVAHjxoJcInKx&users=0, plus a CRLF(Carriage-return and Line feed).

Make sure any strings, like name, are escaped.

If everything goes well, in the response body you'll receive a URL to the server. Otherwise you'll get a nice HTML error message. There aren't any HTML headers to parse, as the HTTP version is not specified so HTTP/0.9 is used, which does not have headers.

User Authentication[]

The "key" provided when a user joins the server can be compared to the MD5 checksum of the server's "salt" plus the username to verify that the user is logged in to minecraft.net with that username. This is useful for establishing enough trust of the name provided to ban or op the player by name.

if( player.key == md5( server.salt + player.name ) ) {
 // player is logged in via minecraft.net
} else {
 // player is forging the username

This is also the way that Notch prevents "cracked," or pirated, clients from accessing online servers. When a cracked client tries to connect to an online server, an error will come up at the connection screen saying, "Failed to Connect: User Not Premium"

Note: This means that you should make sure your "salt" is kept a secret and shared only with heartbeat.jsp. If your server's "salt" is visible anywhere to users, it is trivial for users to produce valid-looking "key"s without being logged in to minecraft.net.

Packet Protocol[]

Every packet starts with a byte representing the Packet ID.

Protocol Data Types[]

Type Size [bytes] Description
Byte 1 Single byte integer (0 to 255)
SByte 1 Single byte signed integer (-128 to 127)
Short 2 Signed integer, network order (-32768 to 32767)
String 64 US-ASCII/ISO646-US encoded string padded with spaces (0x20)
Byte array 1024 Binary data padded with null bytes (0x00)

Client → Server packets[]

Packet ID Purpose Field Description Field Type Notes
0x00 Player Identification Packet ID Byte Sent by a player joining a server with relevant information. Current protocol version is 0x07.
Protocol version Byte
Username String
Verification key String
Unused Byte
0x05 Set Block Packet ID Byte Sent when a user changes a block. The mode field indicates whether a block was created (0x01) or destroyed (0x00).

Block type is always the type player is holding, (even when deleting).

Client assumes that this command packet always succeeds, and so draws the new block immediately. To disallow block creation, server must send back Set Block packet with the old block type.

The XYZ coordinates of the block are just integers representing the coordinate of the block. (As opposed to player coordinates where the lower 5 bits are fractional coordinates)

X Short
Y Short
Z Short
Mode Byte
Block type Byte
0x08 Position and Orientation Packet ID Byte Sent frequently (even while not moving) by the player with the player's current location and orientation. Player ID is always 255, referring to itself. Player coordinates are fixed-point values with the lowest 5 bits representing the fractional position (i.e. divide by 32 to get actual position in terms of block coordinates). The angle parameters are scaled such that a value of 255 would correspond to 360 degrees.
Player ID Byte
X Short
Y Short
Z Short
Yaw (Heading) Byte
Pitch Byte
0x0d Message Packet ID Byte Contain chat messages sent by player.
Unused, maybe message color Byte (0xFF)
Message String

Server → Client packets[]

Packet ID Purpose Field Description Field Type Notes
0x00 Server Identification Packet ID Byte Response to a joining player. The user type indicates whether a player is an op (0x64) or not (0x00) Current protocol version is 0x07.
Protocol version Byte
Server name String
Server MOTD String
User type Byte
0x01 Ping Packet ID Byte Sent to clients periodically. The only way a client can disconnect at the moment is to force it closed, which does not let the server know. The ping packet is used to determine if the connection is still open.
0x02 Level Initialize Packet ID Byte Notifies player of incoming level data.
0x03 Level Data Chunk Packet ID Byte Contains a chunk of gzipped map (not level.dat file). After decompression the map consists of an int(4 bytes) containing number of blocks + raw map array. (chunk is up to 1024 bytes, padded with 0x00s if less).
Chunk Length Short
Chunk Data Byte Array
Percent Complete Byte
0x04 Level Finalize Packet ID Byte Sent after level data is complete and gives map dimensions. The y coordinate is how tall the map is.
X Size Short
Y Size Short
Z Size Short
0x06 Set Block Packet ID Byte Sent to indicate a block change by physics or by players. In the case of a player change, the server will also echo the block change back to the player who initiated it.
X Short
Y Short
Z Short
Block Type Byte
0x07 Spawn Player Packet ID Byte Sent to indicate where a new player is spawning in the world. Position and orientation are encoded the same as for packet 0x08 below.
Player ID SByte
Player Name String
X Short
Y Short
Z Short
Yaw (Heading) Byte
Pitch Byte
0x08 Position and Orientation (Player Teleport) Packet ID Byte Sent with changes in player position and rotation. Teleports player it's sent to if player ID < 0 (For sending initial position in map, and /tp)
Player ID SByte
X Short
Y Short
Z Short
Yaw (Heading) Byte
Pitch Byte
0x09 Position and Orientation Update Packet ID Byte Sent with changes in player position and rotation. Sent when both position and orientation is changed at the same time.

Not required for server operation.

Player ID SByte
Change in X SByte
Change in Y SByte
Change in Z SByte
Yaw (Heading) Byte
Pitch Byte
0x0a Position Update Packet ID Byte Sent with changes in player position.

Not required for server operation.

Player ID SByte
Change in X SByte
Change in Y SByte
Change in Z SByte
0x0b Orientation Update Packet ID Byte Sent with changes in player rotation.

Not required for server operation.

Player ID SByte
Yaw (Heading) Byte
Pitch Byte
0x0c Despawn Player Packet ID Byte Sent when player disconnects.
Player ID SByte
0x0d Message Packet ID Byte Messages sent by chat or from the console.
Player ID SByte
Message String
0x0e Disconnect player Packet ID Byte Sent to a player when they're disconnected from the server.
  1. "Cheat detected: Distance" - happens not only when setting tile too far away from the player (how far is maximum distance and how it is measured?), but also when player moves and then immediately builds.
  2. "Cheat detected: Tile type"
Disconnect reason String
0x0f Update user type Packet ID Byte Sent when a player is opped/deopped

Will give or remove the client's ability of breaking Bedrock blocks

  1. User type can be either 100, which will allow the player, or 0, which will disallow the player to break Bedrock blocks
User type Byte

Player Position[]

Fixed Point[]

Player position is represented via X, Y, and Z fixed-point coordinates. The fractional portion is 5 bits, so dividing the short integers received in position update packets by 32, you will have floating point coordinates for the player. This position corresponds to the center of the client viewport.

Standing On Things[]

The bottom of the player's feet is located 1.59375 (fixed-point: 51) units below the center of the viewport, so to position the player on top of a particular block you could send a teleport (0x08) packet specifying a Y value based on the block position as: (Y x 32 + 51)


A yaw value of 0 means the player is facing in the Z- (negative Z) direction. This value increases in a clockwise direction as seen from above. If we call the negative Z direction "North", then a yaw of 64 means "East", 128 means "South", and 192 means "West".

A pitch value of 0 means level and this value increases in a downward direction. 64 is down, and 192 is up. Values of 65 to 191 should never occur because the player cannot look further up or down than the 64 → 0, 255 → 192 range. However, the Minecraft Classic client does not ignore invalid values, so it is possible to make players' heads "upside-down".

Color codes[]

This article is about classic server protocol. For the updated color codes used in the current version of Minecraft, see Formatting codes.

Messages sent from the server to the client can contain color codes, which allow coloring of text for various purposes.

An ampersand symbol (&) followed by a hex digit in the message tells the client to switch colors while displaying text. The current version of the game uses a section (§) symbol, but the 0.30 version uses ampersands. For the formatting codes for the current version of the game, see Formatting codes.

Color coding at the start of the message will only work if the player ID byte is less than 127. If it's 127 or higher, the game automatically adds &e before the message, making it yellow. However, color codes after the first character still work. If you use an ID below 127, it doesn't add a color code, so the ones you use will work.


Hex digit to color mapping.

Sample Code Common Name Alternate Name Foreground Color Background Color
&0 Black Black 0 0 0 #000 0 0 0 #000000
&1 Dark Blue Navy 0 0 170 #00A 0 0 42 #00002A
&2 Dark Green Green 0 170 0 #0A0 0 42 0 #002A00
&3 Teal Teal 0 170 170 #0AA 0 42 42 #002A2A
&4 Dark Red Maroon 170 0 0 #A00 42 0 0 #2A0000
&5 Purple Purple 170 0 170 #A0A 42 0 42 #2A002A
&6 Dark Yellow Gold 170 170 0 #AA0 42 42 0 #2A2A00
&7 Gray Silver 170 170 170 #AAA 42 42 42 #2A2A2A
&8 Dark Gray Gray 85 85 85 #555 21 21 21 #151515
&9 Indigo Blue 85 85 255 #55F 21 21 63 #15153F
&a Bright Green Lime 85 255 85 #5F5 21 63 21 #153F15
&b Cyan Aqua 85 255 255 #5FF 21 63 63 #153F3F
&c Red Red 255 85 85 #F55 63 21 21 #3F1515
&d Pink Pink 255 85 255 #F5F 63 21 63 #3F153F
&e Yellow Yellow 255 255 85 #FF5 63 63 21 #3F3F15
&f White White 255 255 255 #FFF 63 63 63 #3F3F3F