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

BSON /ˈbsən/ 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, associative arrays (called objects or documents in MongoDB), and various data types of specific interest to MongoDB. The name "BSON" is based on the term JSON and stands for "Binary JSON".[2]

Data types and syntax

BSON documents (objects) consist of an ordered list of elements.[3][4] 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)
  • decimal128 (128-bit IEEE 754-2008 floating point number; Binary Integer Decimal (BID) variant), suitable as a carrier for arbitrary precision numerics with 34 decimal digits of precision, a max value of approximately 106145
  • date (integer number of milliseconds since the Unix epoch)
  • byte array (binary data)
  • boolean (true and false)
  • null
  • BSON object
  • BSON array
  • JavaScript code
  • MD5 binary data
  • Regular expression (Perl compatible regular expressions ("PCRE") version 8.41 with UTF-8 support)[5]

BSON types are nominally a superset of JSON types (JSON does not have a date or a byte array type, for example[6]), 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


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