.BSON

Introduction

BSON is the binary form in which MongoDB stores and sends its documents. It holds the same structure as JSON, objects and arrays of values, and adds types JSON lacks, such as dates, 32-bit and 64-bit integers, decimals, raw binary and MongoDB’s 12-byte ObjectId.

Unlike most compact formats, BSON puts the length in front of every document and string, so a reader can skip over values it does not need. That makes it fast to scan but often larger than JSON. The mongodump tool writes each collection as a .bson file.

Structure

All numbers are little-endian. A document is a 32-bit total length, then its elements, then a zero byte. Each element is a type byte, the field name as a zero-terminated string, and the value. Common types:

A .bson file from mongodump is simply one document after another, with no header.

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