NBT format

The Named Binary Tag (NBT) format is use by Minecraft for the various files in which it saves data. The format is designed to store data in a tree structure made up of various tags. All tags have an ID and a name.

Another more user-friendly format of NBT is in plain string, as used in commands. This format is referred to as SNBT, short for stringified NBT.

SNBT format
SNBT, also known as data tag, is often used in command $$. It can be described starting with attribute-value pairs enclosed in curly braces. One common usage of data tags $$ is in commands, used to specify complex data for any entity.

A data tag consists of zero or more attribute-value pairs delimited by commas and enclosed in curly braces. Each attribute-value pair consists of an tag name and the tag's value, separated by a colon. Some values, however, may be a compound tag and themselves contain attribute-value pairs, allowing a data tag to describe a hierarchical data structure.

Tag's name can be enclosed with double quotes if necessary.

It is different from the JSON format; hence, any JSON used in NBT, such as raw JSON text, must be enclosed within a string tag.


 * Example:

Format of each type
The defined data structures also expect the values to be of the correct type.

Some commands may require that a number's type be specified by adding a letter (B, S, L, F, D) to the end of the value. For example,  for a short,   for a float, etc. (This doesn't work with I for int.) The letter can be uppercase or lowercase. When no letter is used and Minecraft can't tell the type from context, it assumes double if there's a decimal point, int if there's no decimal point and the size fits within 32 bits, or string if neither is true. A square-bracketed literal is assumed to be a list unless an identifier is used:  for an int array and   for a long array.

When commands such as are used to match data tags, they check only for the presence of the provided tags in the target entity/block/item. This means that the entity/block/item can have additional tags and still match. This is true even for lists: the order of a list is not considered, and as long as every requested element is in the list, it matches even if there are additional elements. However, the order and number of elements in a array is acknowledged.

NBT file
An NBT file is a zipped Compound tag, with the name and tag ID included. The file in the zip must contain the Compound tag that it is as the first bytes. Some of the files utilized by Minecraft may be uncompressed, but in most cases, the files follow Notch's original specification and are compressed with GZip.

TAG definition
A tag is an individual part of the data tree. The first byte in a tag is the tag type (ID), followed by a two byte big-endian unsigned integer for the length of the name, then the name as a string in UTF-8 format (Note TAG_End is not named and does not contain the extra 2 bytes; the name is assumed to be empty). Finally, depending on the type of the tag, the bytes that follow are part of that tag's payload. This table describes each of the 13 known tags in version 19133 of the NBT format: The List and Compound tags can be and often are recursively nested. It should also be noted that, in a list of lists, each of the sub-lists can list a different kind of tag.

Usage
Minecraft sometimes uses the NBT format inconsistently; in some instances, empty lists may be represented as a list of Byte tags rather than a list of the correct type, or as a list of End tags in newer versions of Minecraft, which can break some older NBT tools. Additionally, almost every root tag has an empty name string and encapsulates only one Compound tag with the actual data and a name. For instance: Additionally, although the original specification by Notch allows for spaces in tag names, and even the example uses spaces in the tag names, Minecraft has no known files where any tags have spaces in their names. There is also inconsistent use of letter case, mostly either camelCase or PascalCase, but sometimes even in all lowercase.
 * The root tag for most Minecraft NBT structures.
 * : The only tag contained within the root tag - it has a name and contains all the actual data.

Uses

 * level.dat is stored in compressed NBT format.
 * .dat files are stored in compressed NBT format.
 * idcounts.dat is stored in compressed NBT format.
 * villages.dat is stored in compressed NBT format.
 * map_<#>.dat files are stored in compressed NBT format.
 * servers.dat, which is used to store the list of saved multiplayer servers as uncompressed NBT.
 * Chunks are stored in compressed NBT format within Region files.
 * scoreboard.dat is stored in compressed NBT format.
 * Generated structures are stored in compressed NBT format.
 * Saved structures are stored in compressed NBT format.

Official software
Mojang has provided sample Java NBT classes for developers to use and reference as part of the source code for the MCRegion to Anvil file format converter. Since Java Edition 1.13, Minecraft includes a built-in converter between the SNBT format and compressed NBT format, which comes with both the client and official server.

The data generator from Minecraft is able to convert uncompressed Stringified NBT files with .snbt extension in an input folder to GZip compressed NBT format files with .nbt extension in an output folder, and vice versa.

The vanilla data generator can convert any GZip compressed NBT format to SNBT format. The file extension of a file can simply be changed, such as level.dat to level.nbt and put in the input folder, and the generator then decodes the GZip compressed NBT data.

History
The NBT file format was described by Notch in a brief specification.

The original known version was 19132 as introduced in Beta 1.3, and since then has been updated to 19133 with the Anvil file format, which adds the tag. The NBT format dates all the way back to Indev with tags 0 to 10 in use.