BSON Explained

Introduction

BSON stands for Binary JSON. It's the serialization format MongoDB uses to store and transmit documents. BSON is a superset of JSON: it preserves all JSON types and adds binary-friendly types like ObjectId, Date, Decimal128, Binary and Timestamp.

Understanding the topic

Why BSON and not plain JSON?

• Type fidelity — distinguishes int32, int64, double, decimal.
• Native dates — stored as 64-bit ms-since-epoch, queryable with range operators.
• Binary data — store images, hashes, UUIDs efficiently.
• Traversal-friendly — length-prefixed, so the server can skip fields without parsing.
• Compact on the wire compared to text JSON.

Syntax reference

BSON-specific types you'll use often:

ObjectId("66f8a...")        // 12-byte unique id (default _id)
ISODate("2026-06-08T12:00")  // date
NumberLong(9223372036854775807)
NumberDecimal("19.99")       // exact decimal — use for money
UUID("xxxxxxxx-...")          // standardized UUID
BinData(0, "...")            // raw binary

Real-world use

When your API receives JSON and your driver serializes it to BSON, you get accurate dates and decimals automatically — no parsing bugs.

Best practices

• Always use NumberDecimal for currency, never double.
• Use ISODate for timestamps so range queries ($gte, $lt) work natively.
• Use UUID when you need a globally unique id outside MongoDB.