---
obj: format
website: https://msgpack.org
mime: "application/msgpack"
extension: ["mpk", "msgpack"]
---
# MessagePack
MessagePack is an efficient binary serialization format. It lets you exchange data among multiple languages like [JSON](JSON.md). But it's faster and smaller. Small integers are encoded into a single byte, and typical short strings require only one extra byte in addition to the strings themselves.
## Specification
MessagePack has two concepts: type system and formats.
## Types
- Integer represents an integer
- Nil represents nil
- Boolean represents true or false
- Float represents a IEEE 754 double precision floating point number including NaN and Infinity
- Raw
- - String extending Raw type represents a [UTF-8](Unicode.md) string
- - Binary extending Raw type represents a byte array
- Array represents a sequence of objects
- Map represents key-value pairs of objects
- Extension represents a tuple of type information and a byte array where type information is an integer whose meaning is defined by applications or MessagePack specification
- - Timestamp represents an instantaneous point on the time-line in the world that is independent from time zones or calendars. Maximum precision is nanoseconds.
## Formats
### Overview
format name | first byte (in binary) | first byte (in hex)
--------------- | ---------------------- | -------------------
positive fixint | 0xxxxxxx | 0x00 - 0x7f
fixmap | 1000xxxx | 0x80 - 0x8f
fixarray | 1001xxxx | 0x90 - 0x9f
fixstr | 101xxxxx | 0xa0 - 0xbf
nil | 11000000 | 0xc0
(never used) | 11000001 | 0xc1
false | 11000010 | 0xc2
true | 11000011 | 0xc3
bin 8 | 11000100 | 0xc4
bin 16 | 11000101 | 0xc5
bin 32 | 11000110 | 0xc6
ext 8 | 11000111 | 0xc7
ext 16 | 11001000 | 0xc8
ext 32 | 11001001 | 0xc9
float 32 | 11001010 | 0xca
float 64 | 11001011 | 0xcb
uint 8 | 11001100 | 0xcc
uint 16 | 11001101 | 0xcd
uint 32 | 11001110 | 0xce
uint 64 | 11001111 | 0xcf
int 8 | 11010000 | 0xd0
int 16 | 11010001 | 0xd1
int 32 | 11010010 | 0xd2
int 64 | 11010011 | 0xd3
fixext 1 | 11010100 | 0xd4
fixext 2 | 11010101 | 0xd5
fixext 4 | 11010110 | 0xd6
fixext 8 | 11010111 | 0xd7
fixext 16 | 11011000 | 0xd8
str 8 | 11011001 | 0xd9
str 16 | 11011010 | 0xda
str 32 | 11011011 | 0xdb
array 16 | 11011100 | 0xdc
array 32 | 11011101 | 0xdd
map 16 | 11011110 | 0xde
map 32 | 11011111 | 0xdf
negative fixint | 111xxxxx | 0xe0 - 0xff
### Notation in diagrams
one byte:
+--------+
| |
+--------+
a variable number of bytes:
+========+
| |
+========+
variable number of objects stored in MessagePack format:
+~~~~~~~~~~~~~~~~~+
| |
+~~~~~~~~~~~~~~~~~+
`X`, `Y`, `Z` and `A` are the symbols that will be replaced by an actual bit.
### nil format
Nil format stores nil in 1 byte.
nil:
+--------+
| 0xc0 |
+--------+
### bool format family
Bool format family stores false or true in 1 byte.
false:
+--------+
| 0xc2 |
+--------+
true:
+--------+
| 0xc3 |
+--------+
### int format family
Int format family stores an integer in 1, 2, 3, 5, or 9 bytes.
positive fixint stores 7-bit positive integer
+--------+
|0XXXXXXX|
+--------+
negative fixint stores 5-bit negative integer
+--------+
|111YYYYY|
+--------+
* 0XXXXXXX is 8-bit unsigned integer
* 111YYYYY is 8-bit signed integer
uint 8 stores a 8-bit unsigned integer
+--------+--------+
| 0xcc |ZZZZZZZZ|
+--------+--------+
uint 16 stores a 16-bit big-endian unsigned integer
+--------+--------+--------+
| 0xcd |ZZZZZZZZ|ZZZZZZZZ|
+--------+--------+--------+
uint 32 stores a 32-bit big-endian unsigned integer
+--------+--------+--------+--------+--------+
| 0xce |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|
+--------+--------+--------+--------+--------+
uint 64 stores a 64-bit big-endian unsigned integer
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
| 0xcf |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
int 8 stores a 8-bit signed integer
+--------+--------+
| 0xd0 |ZZZZZZZZ|
+--------+--------+
int 16 stores a 16-bit big-endian signed integer
+--------+--------+--------+
| 0xd1 |ZZZZZZZZ|ZZZZZZZZ|
+--------+--------+--------+
int 32 stores a 32-bit big-endian signed integer
+--------+--------+--------+--------+--------+
| 0xd2 |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|
+--------+--------+--------+--------+--------+
int 64 stores a 64-bit big-endian signed integer
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
| 0xd3 |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
### float format family
Float format family stores a floating point number in 5 bytes or 9 bytes.
float 32 stores a floating point number in IEEE 754 single precision floating point number format:
+--------+--------+--------+--------+--------+
| 0xca |XXXXXXXX|XXXXXXXX|XXXXXXXX|XXXXXXXX|
+--------+--------+--------+--------+--------+
float 64 stores a floating point number in IEEE 754 double precision floating point number format:
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
| 0xcb |YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|YYYYYYYY|
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
where
* XXXXXXXX_XXXXXXXX_XXXXXXXX_XXXXXXXX is a big-endian IEEE 754 single precision floating point number.
Extension of precision from single-precision to double-precision does not lose precision.
* YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY_YYYYYYYY is a big-endian
IEEE 754 double precision floating point number
### str format family
Str format family stores a byte array in 1, 2, 3, or 5 bytes of extra bytes in addition to the size of the byte array.
fixstr stores a byte array whose length is upto 31 bytes:
+--------+========+
|101XXXXX| data |
+--------+========+
str 8 stores a byte array whose length is upto (2^8)-1 bytes:
+--------+--------+========+
| 0xd9 |YYYYYYYY| data |
+--------+--------+========+
str 16 stores a byte array whose length is upto (2^16)-1 bytes:
+--------+--------+--------+========+
| 0xda |ZZZZZZZZ|ZZZZZZZZ| data |
+--------+--------+--------+========+
str 32 stores a byte array whose length is upto (2^32)-1 bytes:
+--------+--------+--------+--------+--------+========+
| 0xdb |AAAAAAAA|AAAAAAAA|AAAAAAAA|AAAAAAAA| data |
+--------+--------+--------+--------+--------+========+
where
* XXXXX is a 5-bit unsigned integer which represents N
* YYYYYYYY is a 8-bit unsigned integer which represents N
* ZZZZZZZZ_ZZZZZZZZ is a 16-bit big-endian unsigned integer which represents N
* AAAAAAAA_AAAAAAAA_AAAAAAAA_AAAAAAAA is a 32-bit big-endian unsigned integer which represents N
* N is the length of data
### bin format family
Bin format family stores an byte array in 2, 3, or 5 bytes of extra bytes in addition to the size of the byte array.
bin 8 stores a byte array whose length is upto (2^8)-1 bytes:
+--------+--------+========+
| 0xc4 |XXXXXXXX| data |
+--------+--------+========+
bin 16 stores a byte array whose length is upto (2^16)-1 bytes:
+--------+--------+--------+========+
| 0xc5 |YYYYYYYY|YYYYYYYY| data |
+--------+--------+--------+========+
bin 32 stores a byte array whose length is upto (2^32)-1 bytes:
+--------+--------+--------+--------+--------+========+
| 0xc6 |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ| data |
+--------+--------+--------+--------+--------+========+
where
* XXXXXXXX is a 8-bit unsigned integer which represents N
* YYYYYYYY_YYYYYYYY is a 16-bit big-endian unsigned integer which represents N
* ZZZZZZZZ_ZZZZZZZZ_ZZZZZZZZ_ZZZZZZZZ is a 32-bit big-endian unsigned integer which represents N
* N is the length of data
### array format family
Array format family stores a sequence of elements in 1, 3, or 5 bytes of extra bytes in addition to the elements.
fixarray stores an array whose length is upto 15 elements:
+--------+~~~~~~~~~~~~~~~~~+
|1001XXXX| N objects |
+--------+~~~~~~~~~~~~~~~~~+
array 16 stores an array whose length is upto (2^16)-1 elements:
+--------+--------+--------+~~~~~~~~~~~~~~~~~+
| 0xdc |YYYYYYYY|YYYYYYYY| N objects |
+--------+--------+--------+~~~~~~~~~~~~~~~~~+
array 32 stores an array whose length is upto (2^32)-1 elements:
+--------+--------+--------+--------+--------+~~~~~~~~~~~~~~~~~+
| 0xdd |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ| N objects |
+--------+--------+--------+--------+--------+~~~~~~~~~~~~~~~~~+
where
* XXXX is a 4-bit unsigned integer which represents N
* YYYYYYYY_YYYYYYYY is a 16-bit big-endian unsigned integer which represents N
* ZZZZZZZZ_ZZZZZZZZ_ZZZZZZZZ_ZZZZZZZZ is a 32-bit big-endian unsigned integer which represents N
* N is the size of an array
### map format family
Map format family stores a sequence of key-value pairs in 1, 3, or 5 bytes of extra bytes in addition to the key-value pairs.
fixmap stores a map whose length is upto 15 elements
+--------+~~~~~~~~~~~~~~~~~+
|1000XXXX| N*2 objects |
+--------+~~~~~~~~~~~~~~~~~+
map 16 stores a map whose length is upto (2^16)-1 elements
+--------+--------+--------+~~~~~~~~~~~~~~~~~+
| 0xde |YYYYYYYY|YYYYYYYY| N*2 objects |
+--------+--------+--------+~~~~~~~~~~~~~~~~~+
map 32 stores a map whose length is upto (2^32)-1 elements
+--------+--------+--------+--------+--------+~~~~~~~~~~~~~~~~~+
| 0xdf |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ| N*2 objects |
+--------+--------+--------+--------+--------+~~~~~~~~~~~~~~~~~+
where
* XXXX is a 4-bit unsigned integer which represents N
* YYYYYYYY_YYYYYYYY is a 16-bit big-endian unsigned integer which represents N
* ZZZZZZZZ_ZZZZZZZZ_ZZZZZZZZ_ZZZZZZZZ is a 32-bit big-endian unsigned integer which represents N
* N is the size of a map
* odd elements in objects are keys of a map
* the next element of a key is its associated value
### ext format family
Ext format family stores a tuple of an integer and a byte array.
fixext 1 stores an integer and a byte array whose length is 1 byte
+--------+--------+--------+
| 0xd4 | type | data |
+--------+--------+--------+
fixext 2 stores an integer and a byte array whose length is 2 bytes
+--------+--------+--------+--------+
| 0xd5 | type | data |
+--------+--------+--------+--------+
fixext 4 stores an integer and a byte array whose length is 4 bytes
+--------+--------+--------+--------+--------+--------+
| 0xd6 | type | data |
+--------+--------+--------+--------+--------+--------+
fixext 8 stores an integer and a byte array whose length is 8 bytes
+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+
| 0xd7 | type | data |
+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+
fixext 16 stores an integer and a byte array whose length is 16 bytes
+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+
| 0xd8 | type | data
+--------+--------+--------+--------+--------+--------+--------+--------+--------+--------+
+--------+--------+--------+--------+--------+--------+--------+--------+
data (cont.) |
+--------+--------+--------+--------+--------+--------+--------+--------+
ext 8 stores an integer and a byte array whose length is upto (2^8)-1 bytes:
+--------+--------+--------+========+
| 0xc7 |XXXXXXXX| type | data |
+--------+--------+--------+========+
ext 16 stores an integer and a byte array whose length is upto (2^16)-1 bytes:
+--------+--------+--------+--------+========+
| 0xc8 |YYYYYYYY|YYYYYYYY| type | data |
+--------+--------+--------+--------+========+
ext 32 stores an integer and a byte array whose length is upto (2^32)-1 bytes:
+--------+--------+--------+--------+--------+--------+========+
| 0xc9 |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ| type | data |
+--------+--------+--------+--------+--------+--------+========+
where
* XXXXXXXX is a 8-bit unsigned integer which represents N
* YYYYYYYY_YYYYYYYY is a 16-bit big-endian unsigned integer which represents N
* ZZZZZZZZ_ZZZZZZZZ_ZZZZZZZZ_ZZZZZZZZ is a big-endian 32-bit unsigned integer which represents N
* N is a length of data
* type is a signed 8-bit signed integer
* type < 0 is reserved for future extension including 2-byte type information
### Timestamp extension type
Timestamp extension type is assigned to extension type `-1`. It defines 3 formats: 32-bit format, 64-bit format, and 96-bit format.
timestamp 32 stores the number of seconds that have elapsed since 1970-01-01 00:00:00 UTC
in an 32-bit unsigned integer:
+--------+--------+--------+--------+--------+--------+
| 0xd6 | -1 | seconds in 32-bit unsigned int |
+--------+--------+--------+--------+--------+--------+
timestamp 64 stores the number of seconds and nanoseconds that have elapsed since 1970-01-01 00:00:00 UTC
in 32-bit unsigned integers:
+--------+--------+--------+--------+--------+------|-+--------+--------+--------+--------+
| 0xd7 | -1 | nanosec. in 30-bit unsigned int | seconds in 34-bit unsigned int |
+--------+--------+--------+--------+--------+------^-+--------+--------+--------+--------+
timestamp 96 stores the number of seconds and nanoseconds that have elapsed since 1970-01-01 00:00:00 UTC
in 64-bit signed integer and 32-bit unsigned integer:
+--------+--------+--------+--------+--------+--------+--------+
| 0xc7 | 12 | -1 |nanoseconds in 32-bit unsigned int |
+--------+--------+--------+--------+--------+--------+--------+
+--------+--------+--------+--------+--------+--------+--------+--------+
seconds in 64-bit signed int |
+--------+--------+--------+--------+--------+--------+--------+--------+
* Timestamp 32 format can represent a timestamp in [1970-01-01 00:00:00 UTC, 2106-02-07 06:28:16 UTC) range. Nanoseconds part is 0.
* Timestamp 64 format can represent a timestamp in [1970-01-01 00:00:00.000000000 UTC, 2514-05-30 01:53:04.000000000 UTC) range.
* Timestamp 96 format can represent a timestamp in [-292277022657-01-27 08:29:52 UTC, 292277026596-12-04 15:30:08.000000000 UTC) range.
* In timestamp 64 and timestamp 96 formats, nanoseconds must not be larger than 999999999.