Data types

This article defines the data types used in the protocol. All data sent over the network (except for VarInt and VarLong) is big-endian, that is the bytes are sent from most significant byte to least significant byte. The majority of everyday computers are little-endian, therefore it may be necessary to change the endianness before sending data over the network.

Definitions

Name	Size (bytes)	Encodes	Notes
Boolean	1	Either false or true	True is encoded as 0x01, false as 0x00.
Byte	1	An integer between -128 and 127	Signed 8-bit integer, two's complement
Unsigned Byte	1	An integer between 0 and 255	Unsigned 8-bit integer
Short	2	An integer between -32768 and 32767	Signed 16-bit integer, two's complement
Unsigned Short	2	An integer between 0 and 65535	Unsigned 16-bit integer
Int	4	An integer between -2147483648 and 2147483647	Signed 32-bit integer, two's complement
Long	8	An integer between -9223372036854775808 and 9223372036854775807	Signed 64-bit integer, two's complement
Float	4	A single-precision 32-bit IEEE 754 floating point number
Double	8	A double-precision 64-bit IEEE 754 floating point number
String	≥ 1 ≤ 2147483652	A sequence of Unicode scalar values	UTF-8 string prefixed with its size in bytes as a VarInt
Chat	≥ 1 ≤ 2147483652	See Chat	Encoded as a String
VarInt	≥ 1 ≤ 5	An integer between -2147483648 and 2147483647	Protocol Buffer Varint, encoding a two's complement signed 32-bit integer
VarLong	≥ 1 ≤ 10	An integer between -9223372036854775808 and 9223372036854775807	Protocol Buffer Varint, encoding a two's complement signed 64-bit integer
Chunk Section	Varies	A 16×16×16 chunk of blocks	See SMP Map Format
Entity Metadata	Varies	Miscellaneous information about an entity	See Entities#Entity Metadata Format
Slot	Varies	An item stack in an inventory or container	See Slot Data
NBT Tag	Varies	Depends on context	See NBT
Position	8	An integer/block position: x (-33554432 to 33554431), y (-2048 to 2047), z (-33554432 to 33554431)	x as a 26-bit integer, followed by y as a 12-bit integer, followed by z as a 26-bit integer (all signed, two's complement). See also the section below.
Angle	1	A rotation angle in steps of 1/256 of a full turn	Whether or not this is signed does not matter, since the resulting angles are the same.
UUID	16	A UUID	Encoded as an unsigned 64-bit integer
Optional X	0 or size of X	A field of type X, or nothing	Whether or not the field is present must be known from the context.
Array of X	count times size of X	Zero or more fields of type X	The count must be known from the context.
X Enum	size of X	A specific value from a given list	The list of possible values and how each is encoded as an X must be known from the context.
Byte Array	Varies	Depends on context	This is just a sequence of zero or more bytes, its meaning should be explained somewhere else, e.g. in the packet description. The length must also be known from the context.

Position

64-bit value split in to three parts

• x: 26 MSBs
• z: 26 LSBs
• y: 12 bits between them

Encoded as followed:

((x & 0x3FFFFFF) << 38) | ((y & 0xFFF) << 26) | (z & 0x3FFFFFF)

And decoded as:

val = read_unsigned_long();
x = val >> 38;
y = (val >> 26) & 0xFFF;
z = val << 38 >> 38;

Note: The details of bit shifting are rather language dependent; the above may work in Java but probably won't in other languages without some tweaking. In particular, you will usually receive positive numbers even if the actual coordinates are negative. This can be fixed by adding something like the following:

if x >= 2^25 { x -= 2^26 }
if y >= 2^11 { y -= 2^12 }
if z >= 2^25 { z -= 2^26 }

Fixed-point numbers

Some fields may be stored as fixed-point numbers, where a certain number of bits represents the signed integer part (number to the left of the decimal point) and the rest represents the fractional part (to the right). Floating points (float and double), in contrast, keep the number itself (mantissa) in one chunk, while the location of the decimal point (exponent) is stored beside it.

Essentially, while fixed-point numbers have lower range than floating points, their fractional precision is greater for higher values. This makes them ideal for representing global coordinates of an entity in Minecraft, as it's more important to store the integer part accurately than position them more precisely within a single block (or meter).

Coordinates are often represented as a 32-bit integer, where 5 of the least-significant bits are dedicated to the fractional part, and the rest store the integer part.

Java lacks support for fractional integers directly, but you can represent them as integers. To convert from a double to this integer representation, use the following formulas:

 abs_int = (int)double * 32;

And back again:

 double = (double)abs_int / 32;