NBT format

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The Named Binary Tag format is used by Minecraft for the various files in which it saves data. The format is described by Notch in a very brief specification. The format is designed to store data in a tree structure made up of various tags. All tags have an ID and a name. The original known version was 19132 as introduced in Beta 1.3, and since then has been updated to 19133 with Anvil, with the addition of the Int Array tag. The NBT format dates all the way back to Indev with tags 0 to 10 in use.

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. 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.

TAG definition[edit]

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). The name of tags may contain spaces, although Minecraft itself never saves tags with spaces in the names. 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 Named Binary Tag format:

ID Icon Tag Type Payload SNBT Format‌[JE only] Description Storage Capacity
0 TAG_End None. - Used to mark the end of compound tags. This tag does not have a name, so it is only ever a single byte 0. It may also be the type of empty List tags. N/A
1 TAG_Byte 1 byte / 8 bits, signed <number>b or <number>B A signed integral type. Sometimes used for booleans. Full range of -(27) to (27 - 1)
(-128 to 127)
2 TAG_Short 2 bytes / 16 bits, signed, big endian <number>s or <number>S A signed integral type. Full range of -(215) to (215 - 1)
(-32,768 to 32,767)
3 TAG_Int 4 bytes / 32 bits, signed, big endian <number> A signed integral type. Full range of -(231) to (231 - 1)
(-2,147,483,648 to 2,147,483,647)
4 TAG_Long 8 bytes / 64 bits, signed, big endian <number>l or <number>L A signed integral type. Full range of -(263) to (263 - 1)
(-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807)
5 TAG_Float 4 bytes / 32 bits, signed, big endian, IEEE 754-2008, binary32 <number>f or <number>F A signed floating point type. Precision varies throughout number line;
See Single-precision floating-point format. Maximum value about 3.4*1038
6 TAG_Double 8 bytes / 64 bits, signed, big endian, IEEE 754-2008, binary64 <decimal number>, <number>d or <number>D A signed floating point type. Precision varies throughout number line;
See Double-precision floating-point format. Maximum value about 1.8*10308
7 TAG_Byte_Array TAG_Int's payload size, then size TAG_Byte's payloads. [B;<byte>,<byte>,...] An array of bytes. Maximum number of elements ranges between (231 - 9) and (231 - 1) (2,147,483,639 and 2,147,483,647), depending on the specific JVM.
8 TAG_String TAG_Short's payload length, then a UTF-8 string with size length. <a-zA-Z0-9 text>, "<text>" (" within needs to be escaped to \"), or '<text>' (' within needs to be escaped to \') A UTF-8 string. It has a size, rather than being null terminated. 32,767 bytes interpretable as UTF-8 (see UTF-8 format; most commonly-used characters are a single byte).
9 TAG_List TAG_Byte's payload tagId, then TAG_Int's payload size, then size tags' payloads, all of type tagId. [<value>,<value>,...] A list of tag payloads, without repeated tag IDs or any tag names. Due to JVM limitations and the implementation of ArrayList, the maximum number of list elements is (231 - 9), or 2,147,483,639. Also note that List and Compound tags may not be nested beyond a depth of 512.
10 TAG_Compound Fully formed tags, followed by a TAG_End. {<tag name>:<value>,<tag name>:<value>,...} A list of fully formed tags, including their IDs, names, and payloads. No two tags may have the same name. Unlike lists, there is no hard limit to the number of tags within a Compound (of course, there is always the implicit limit of virtual memory). Note, however, that Compound and List tags may not be nested beyond a depth of 512.
11 TAG_Int_Array TAG_Int's payload size, then size TAG_Int's payloads. [I;<integer>,<integer>,...] An array of TAG_Int's payloads. Maximum number of elements ranges between (231 - 9) and (231 - 1) (2,147,483,639 and 2,147,483,647), depending on the specific JVM.
12 TAG_Long_Array TAG_Int's payload size, then size TAG_Long's payloads. [L;<long>,<long>,...] An array of TAG_Long's payloads. Maximum number of elements ranges between (231 - 9) and (231 - 1) (2,147,483,639 and 2,147,483,647), depending on the specific JVM.

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.

File Format[edit]

An NBT file is a GZip'd Compound tag, name and tag ID included. 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. In the Legacy Console Edition, chunks are compressed with XMemCompress, a variation of an LZX compression algorithm. There is no header to specify the version or any other information - only the level.dat file specifies the version.

As used in Minecraft[edit]

Minecraft's use of the NBT format is odd at times. 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:

  • The root tag for most Minecraft NBT structures.
    •  SomeName: The only tag contained within the root tag - it has a name and contains all the actual data.

Another noticeable oddity is that, 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.


This section is a stub, meaning that it lacks some important information. You can help by expanding it with further information relating to the topic.
Reason: Doesn't describe Bedrock Edition.


Mojang has provided sample Java NBT classes for developers to use and reference as part of the source code for the McRegion -> Anvil converter. Since 1.13, Minecraft includes a builtin converter between SNBT format and compressed NBT format. It comes with the client and the official server.[1]


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. You can simply change the file extension of a file, such as level.dat to level.nbt and put it in the input folder, and the generator will decode the GZip compressed NBT data.


The community has developed programs to view and modify compressed and uncompressed NBT files:

Name NBT Version Description Screenshot
CL-NBT 19132 CL-NBT is an NBT implementation in Common Lisp that can read and write NBT files and load and save McRegion files. Anvil format works with slight modification.
MineBack Ultimate 19133 MineBack Ultimate provides a full NBT editor supporting all available types of NBT format file (Map, Level, World etc.). It comes with a modern GUI and many helper functions. MineBackNBTEditor.png
NBT for Python 19133 Library to parse & write NBT files, both standalone or in region files, in the Python scripting language. Provided with application examples for inspecting & editing the Minecraft data files (block / chest / mobs statistics and simple world mapping). Supports old McRegion, pre-flattened and latest Anvil formats.
NBTEdit 19132 Allows for viewing and modifying NBT files via a Windows tree control. It is outdated not only from being an NBT version behind, but because it does not support multiple tags with the same name and it forces incorrect ranges on some types, and it lacks support for uncompressed NBT files. NBTEdit Level.Dat.png
NBTExplorer - Forum Post 19133 Inspired by and based on NBTEdit, this program allows viewing and editing of NBT files via a Windows tree control. It supports compressed and uncompressed NBT files, and allows for direct editing of the NBT structures in MCRegion and Anvil files, level.dat, etc. NBTExplorer.png
NBT grammar for Synalyze It! 19132 Using this grammar Synalyze It! displays a color-coded hex dump along with the parsed tag tree. Currently only uncompressed files are supported. Synalyze-It-NBT-decoded.png
NEINedit 19132 NBT editor for mac with a text-based tree structure. NEINedit.png
NBT2YAML 19133 nbt2yaml presents a command line interface for reading and editing Minecraft NBT files using a custom YAML format. It also includes a Python API for parsing and writing NBT files to/from a simple Python data structure.
webNBT 19133 webNBT is an NBT-editor that runs in modern browsers without requiring the user to download an application or use third-party browser plugins (like Flash or Java).


Java Edition
1.0.0September 28, 2011Notch works on "saving arbitrary data with item instances."
1.12?Added long array tags.
1.1318w01aAdded a data generator to both the Minecraft client and the default multiplayer software.
1.1419w08a String tags can now be within single quotes ' besides double quotes ".[2]