JSON vs BSON

Introduction

JSON is the universal data interchange format of the web. BSON is its binary cousin, optimized for storage and traversal. MongoDB drivers transparently convert between JSON in your code and BSON on the wire — but the differences matter when you debug, serialize, or migrate data.

Understanding the topic

Key differences:

• JSON — text, human-readable, type-poor (everything number is a float).
• BSON — binary, fast to parse, type-rich (int32, int64, decimal, date, binary).
• JSON can't represent dates or binary natively — BSON can.
• BSON is length-prefixed: the server can skip fields without parsing them.
• Drivers convert automatically — you almost always write JSON-like syntax.

Syntax reference

// JSON
{ "createdAt": "2026-06-08T12:00:00Z", "price": 9.99 }

// BSON (logically)
{ createdAt: ISODate("2026-06-08T12:00:00Z"),
  price: NumberDecimal("9.99") }

Real-world use

Export your data with mongoexport — you get Extended JSON, a textual encoding of BSON that preserves all the type info.

Best practices

• Use Extended JSON for backups + migrations.
• Don't round-trip BSON through plain JSON — you'll lose types.