MQTT Payload Formats: JSON, Binary, and Protobuf for IIoT

Choosing the payload format impacts performance, interoperability, and ease of development.

JSON (Plain Text)

• Lightweight and human-readable; ideal for prototypes and debugging.
• Widely supported across all languages.
• Cons: larger size, slower parsing.

{"sensor_id":"S1","value":23.5,"unit":"°C"}

Binary

• Smaller size; useful on bandwidth-constrained links.
• Use struct or C structs to define the layout.
• Cons: less readable, risk of endianness errors.

import struct
# sensor_id:uint8, value:float32
payload = struct.pack('<Bf', 1, 23.5)

Protobuf

• Strongly typed, compact structures.
• Define a schema in .proto and generate client/server code.
• Cons: requires code generation and version management.

.proto:

syntax = "proto3";
message SensorData {
  uint32 sensor_id = 1;
  float value = 2;
  string unit = 3;
}

from sensor_pb2 import SensorData
msg = SensorData(sensor_id=1, value=23.5, unit="°C")
payload = msg.SerializeToString()

In the next post, we’ll analyze the differences between MQTT v3.1.1 and v5, and how to leverage the latest version’s new features.