NBT format

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The Named Binary Tag (NBT) is a tree data structure used by Minecraft in many save files to store arbitrary data. The format is comprised of a handful of tags. Tags have a numeric ID, a name, and a payload. A user-accessible version in the form of strings is the stringified Named Binary Tag (SNBT) format.

History[edit | edit source]

The NBT file format was described by Notch in a brief specification.[1]

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 Int Array tag. The NBT format dates all the way back to Indev with tags 0 to 10 in use.

Java Edition
1.0.0September 28, 2011Notch works on "saving arbitrary data with item instances."
1.814w03aNBT data now supports using string IDs rather than numerical IDs.
1.1217w18aAdded long array tags.
1.1318w01aAdded a data generator to both the Minecraft client and the default multiplayer software.
1.1419w08a String tags and names of tags in compound in SNBT can now be within single quotes ' in addition to double quotes ".[2]
1.1620w21aAdded conversion function between NBT and JSON.

SNBT format[edit | edit source]

This feature is exclusive to Java Edition. 

SNBT, also known as a data tag, is often used in commands in Java Edition. It can be described starting with key-value pairs enclosed in curly braces. An example of SNBT is specifying complex data for entities with commands.

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 a 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.

Example: {name1:123,name2:"sometext1",name3:{subname1:456,subname2:"sometext2"}}

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.

Data types[edit | edit source]

Data Tags Value Types
Type Description SNBT Format SNBT Example
 Byte A signed 8-bit integer, ranging from -128 to 127 (inclusive). <number>b or <number>B 34B, -20b
 Boolean NBT has no boolean data type, but byte value 0 and 1 can be represented as true, false. When a byte field is used as a boolean value, icon is shown. true, false true
 Short A signed 16-bit integer, ranging from -32,768 to 32,767 (inclusive). <number>s or <number>S 31415s, -27183s
 Int A signed 32-bit integer, ranging from -2,147,483,648 and 2,147,483,647 (inclusive). <integer_number> 31415926
 Long A signed 64-bit integer, ranging from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 (inclusive). <number>l or <number>L 31415926l
 Float A 32-bit, single-precision floating-point number, ranging from -3.4E+38 to +3.4E+38.

See IEEE floating point for details.

<number>f or <number>F 3.1415926f
 Double A 64-bit, double-precision floating-point, ranging from -1.7E+308 to +1.7E+308.

See IEEE floating point for details.

<decimal_number>, <number>d or <number>D 3.1415926
 String A sequence of characters A string enclosed in quotes. For strings containing only 0-9, A-Z, a-z, _, -, ., and +, and not confused with other data types, quote enclosure is optional. Quotes can be either single quote ' or double ". Nested quotes can be included within a string by escaping the character with a \ escape. \s that are supposed to show up as \ need to be escaped to \\.

<[a-zA-Z0-9_\-\.\+] text>, "<text>" (" within needs to be escaped to \"), or '<text>' (' within needs to be escaped to \')

"Call me \"Ishmael\""

'Call me "Ishmael"'

'Call me \'Ishmael\''

"Call me 'Ishmael'"

 List An ordered list of tags. The tags must be of the same type, determined by the first tag in the list. Unnamed tags enclosed in square brackets and delimited by commas.

[<value>,<value>,...]

[3.2,64.5,129.5]
 Compound An ordered list of attribute-value pairs.

Each tag can be of any type.

Named tags enclosed in curly braces and delimited by commas.

The key (tag name) can be unquoted if it contains only 0-9, A-Z, a-z, _, -, ., and +. Otherwise the key should be quoted. Quotes can be either single quote ' or double ". Nested quotes can be included within a string by escaping the character with a \ escape. \s that are supposed to show up as \ need to be escaped to \\.

{<[a-zA-Z0-9_\-\.\+] tag_name>:<value>,"<tag name>":<value>,...}

{X:3,Y:64,Z:129}
 Byte Array An ordered list of 8-bit integers. Note that [B;1b,2b,3b] and [1b,2b,3b] are considered different types: the second one is a  list. B; followed by an ordered list of byte tags, delimited by commas. Tag is enclosed in square brackets.

[B;<byte>b,<byte>B,true,false...]

[B;1b,2b,3b]
 Int Array An ordered list of 32-bit integers. Note that [I;1,2,3] and [1,2,3] are considered different types: the second one is a  list. I; followed by an ordered list of int tags, delimited by commas. Tag is enclosed in square brackets.

[I;<integer>,<integer>,...]

[I;1,2,3]
 Long Array An ordered list of 64-bit integers. Note that [L;1l,2l,3l] and [1l,2l,3l] are considered different types: the second one is a  list. L; followed by an ordered list of long tags, delimited by commas. Tag is enclosed in square brackets.

[L;<long>l,<long>L,...]

[L;1l,2l,3l]

NBT object[edit | edit source]

When the game is running, entities and block entities in loading chunks are stored in the memory. They are not stored with NBT, instead, they are just programmatic objects.

When processing NBT operations, the game needs to generate programmatic NBT object from entities/block entities, parse SNBT into NBT object, modify entities/blocks based on provided NBT object, or convert NBT object into SNBT.

Generating NBT object[edit | edit source]

When generating NBT from an entity/block, the entity/block's properties are added into programmatic NBT object.

Note that not all properties are added. For example, the value of whether a player is opening a chest won't be added into NBT object.

A value is added with certain data type. For example, a resource location is converted to a string value.

These NBT objects are also stored into game's save files as NBT files when the game quits or automatically saves. So the data structures that NBT tags describe and the data type for each tag are basically the same ones used in game's save files. These data structures are described in other articles and commands expect data tags to use the same attribute names (which are case-sensitive):

Data Structure Specification Links
Objects Examples
Block entities chests, furnaces, command blocks, mob spawners, signs, etc.
Items items in inventories (includes specifications for enchantments, lore, custom names, etc.)
Item entities items on the ground
Mobs creepers, cows, villagers, etc.
Projectiles arrows, fireballs, thrown potions, etc.
Vehicles boats, minecarts, etc.
Dynamic tiles primed TNT, falling sand/gravel/concrete powder/anvils
Other entities firework rockets, paintings, and item frames

Conversion to SNBT[edit | edit source]

This feature is exclusive to Java Edition. 

A programmatic NBT object would be converted to a SNBT when trying to get it with /data get etc.

After converted, a number is always followed by a letter (lowercase for b, s, f, d, and uppercase for L) except  Integer. For example, 3s for a short, 3.2f for a float, etc.

And a string is always enclosed by double or single quotes.

Other data types are expressed as the #Data types table above.

Conversion from SNBT[edit | edit source]

This feature is exclusive to Java Edition. 

An SNBT is converted to a programmatic NBT object when parsed by the game.

A number that followed by a letter (B, S, L, F, D, or their lowercase) is resolved to corresponding data type. For example, 3s for a short, 3.2f for a float, etc. The letter can be uppercase or lowercase. When no letter is used, 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: [B;1B,2B,3B] for a byte array, [I;1,2,3] for an int array and [L;1L,2L,3L] for a long array.

true and false are converted as 1b and 0b respectively.

Modifying entity/block based on NBT object[edit | edit source]

This feature is exclusive to Java Edition. 

Modifying entity/block based on a programmatic NBT object is not a simple progress. All certain tags need to be resolved before changing properties of a block/entity. Note that only certain properties can be changed. For example, when using /data command to modify a block entity, its coordinates cannot be changed.

If a property needs a value of resource location and gets a  string tag, the string is converted to a resource location.

If a property needs a value of JSON text and gets a  string tag, the string is parsed into JSON text object.

If a property needs a boolean value and gets a numeric tag, true if the number is not 0 after some rounding operation and conversion to byte.

If a property needs a boolean value and gets a non-numeric tag, the property becomes false.

If a property needs a numeric value of certain type and gets a numeric tag of wrong type, the value gets some rounding operation and converts to the required type.

If a property needs a numeric value and gets a non-numeric tag, the number becomes 0.

If a property needs a string value and gets a non-string tag, the string becomes an empty string.

If a property needs a list or array of certain type and gets a wrong-type tag, an empty list/array is got.

If a property needs a compound tag and gets a non-compound tag, an empty compound tag is got.

Testing NBT tags[edit | edit source]

This feature is exclusive to Java Edition. 

When commands such as /clear, /execute if data are used to match data tags, or nbt argument in target selector tries to target entity, the game converts SNBT into programmatic NBT object and gets programmatic NBT object from block/entity/storage, then compares the two NBT objects.

They check only for the presence of the provided tags in the target entity/block/storage. This means that the entity/block/storage can have additional tags and still match. This is true even for lists: the order and number of elements in a list are not considered, and as long as every requested element is in the list, it matches even if there are additional elements. For example, an entity with data {Pos:[1d,2d,3d],Tags:["a","b"]} can be targeted by @e[nbt={Pos:[3d,2d,1d]}] or even just @e[nbt={Pos:[2d]}] even though the former represents a totally different position and the latter is not a valid position at all. Note that @e[nbt={Tags:[]}] can't match it, because an empty list can match only an empty list.

However, the order and number of elements in a byte/long/int array is acknowledged.

The requested data tags in the target entity/block/storage must match exactly for the provided tags to pass, including the data type (e.g. 1, an int, does not match 1d, a double). Namespaces also can't omitted because in NBT object it is just a plain string that won't be resolved into a resource location (e.g. @e[nbt={Item:{id:"stone"}}] does not match a stone item entity, it must be @e[nbt={Item:{id:"minecraft:stone"}}]). The same is true for string of JSON text, which must be exactly the same to match the provided tag (e.g. @e[nbt={CustomName:'"a"'}] does not match any entity, it must be @e[nbt={CustomName:"{\"text\":\"a\"}"}] or @e[nbt={CustomName:'{"text":"a"}'}]).

Binary format[edit | edit source]

An NBT file is a zipped Compound tag. 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[edit | edit source]

Note: Since 1.20.1 NBT sent over the network does not contain the 2 bytes for the length of the root tag

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 (ushort) 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:

ID Icon Tag Type Payload Description Storage Capacity
0 TAG_End - Used to mark the end of compound tags. This tag does not have a name, so it is always a single byte 0. It may also be the type of empty List tags. N/A
1 TAG_Byte 1 byte / 8 bits, signed 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 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 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 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 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 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 A signed integer (4 bytes) size, then the bytes comprising an array of length size. 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 An unsigned short (2 bytes)[3] payload length, then a UTF-8 string resembled by length bytes. A UTF-8 string. It has a size, rather than being null terminated. 65,535 bytes interpretable as UTF-8 (see modified UTF-8 format; most commonly-used characters are a single byte).
9 TAG_List A byte denoting the tag ID of the list's contents, followed by the list's length as a signed integer (4 bytes), then length number of payloads that correspond to the given tag ID. A list of tag payloads, without tag IDs or names, apart from the one before the length. 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. 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 A signed integer size, then size number of TAG_Int's payloads. 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 A signed integer size, then size number of TAG_Long's payloads. 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.

Usage[edit | edit source]

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.

In most cases, the files follow Notch's original specification and are compressed with GZip. But some of the files utilized by Minecraft may be uncompressed, or with zlib (aka DEFLATE with a few bytes extra).

All NBT files created by Minecraft have either a  compound or sometimes a  list‌[Bedrock Edition only] as the root tag, this tag has a name but is often the empty string.

In Bedrock Edition, all numbers are encoded in little-endian. This includes the size prefix before tag names,  string values and  list or  array values, as well as values in all numeric tags.

In Bedrock Edition, the level.dat is uncompressed NBT file with an 8-byte header, consisting of a little-endian 4-byte integer indicating the version of the tool used to save the file. It is followed by another integer containing the length of the file, minus the header.

Uses[edit | edit source]

This section is missing information about: Bedrock Edition NBTs. 
Please expand the section to include this information. Further details may exist on the talk page.

JSON and NBT[edit | edit source]

JSON is a lightweight text-based data-interchange format. The standard of JSON text is specified at ECMA-404. See also JSON.

JSON is very different from NBT. NBT is a data structure which can be represented by binary file or string. JSON is a text format for data-interchange. There are only six data types in JSON: JsonString, JsonNumber, JsonBoolean, JsonNull, JsonObject, and JsonArray. In NBT, there're more types for different numbers, and there're no null and boolean data types. In NBT, there're list, byte array, int array and long array, and elements in a list or an array must be in the same type. However, in JSON, there's only JsonArray, in which elements can be in different data types. The key of a tag in SNBT is allowed to be unquoted, while the key of a name-value pair in JSON must be double-quoted.

So conversion between NBT and JSON may lose a lot of information, and at the same time add a lot of redundant information. However, the conversion is sometimes used by vanilla game in Java Edition. Currently used in custom biome's ambient particle and processor list's "rule" processor type. Below is how the vanilla game converts them.

Conversion from JSON[edit | edit source]

This feature is exclusive to Java Edition. 

Conversion to JSON[edit | edit source]

This feature is exclusive to Java Edition. 

Official software[edit | edit source]

See also: Tutorials/Running the Data Generator

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.[4] 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.[5]

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.

References[edit | edit source]

  1. ↑ http://web.archive.org/web/20110723210920/http://www.minecraft.net/docs/NBT.txt specification
  2. ↑ "Allow single quote in strings by boq · Pull Request #52" – Mojang/brigadier – GitHub.
  3. ↑ https://docs.oracle.com/javase/8/docs/api/java/io/DataOutput.html#writeUTF-java.lang.String-
  4. ↑ https://web.archive.org/web/0/https://www.mojang.com/2012/02/new-minecraft-map-format-anvil/
  5. ↑ https://wiki.vg/Data_Generators#NBT_converters

External links[edit | edit source]

  • nbt, Java library for working with the NBT format.
  • NBT on wiki.vg
  • NBTExplorer, a tool for viewing and editing NBT files.
  • NBT Studio, successor to NBTExplorer that includes additional features like Bedrock support and SNBT.
  • webNBT, an online tool for viewing and editing NBT files.
  • XNBTEdit, XML NBT editor and converter.

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