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Filename extension .bson
Internet media type none[1]
Type of format Data interchange
Extended from JSON
Standard no RFC yet

BSON /ˈbsɒn/ is a computer data interchange format used mainly as a data storage and network transfer format in the MongoDB database. It is a binary form for representing simple data structures and associative arrays (called objects or documents in MongoDB). The name "BSON" is based on the term JSON and stands for "Binary JSON".[2]

Data types and syntax[edit]

BSON documents (objects) consist of an ordered list of elements. Each element consists of a field name, a type, and a value. Field names are strings. Types include:

  • string
  • integer (32- or 64-bit)
  • double (64-bit IEEE 754 floating point number)
  • date (integer number of milliseconds since the Unix epoch)
  • byte array (binary data)
  • boolean (true and false)
  • null
  • BSON object
  • BSON array

BSON types are nominally a superset of JSON types (JSON does not have a date or a byte array type, for example[3]), with one exception of not having a universal "number" type as JSON does.


Compared to JSON, BSON is designed to be efficient both in storage space and scan-speed. Large elements in a BSON document are prefixed with a length field to facilitate scanning. In some cases, BSON will use more space than JSON due to the length prefixes and explicit array indices.[2]


A document such as {"hello":"world"} will be stored as:

  \x16\x00\x00\x00               // total document size
  \x02                           // 0x02 = type String
  hello\x00                      // field name
  \x06\x00\x00\x00world\x00      // field value (size of value, value, null terminator)
  \x00                           // 0x00 = type EOO ('end of object')

See also[edit]


External links[edit]