JSON to Protobuf Converter

Example: JSON input and real Protobuf output

The output below was generated by the same conversion code the converter uses, run on this sample when the page was built.

{
  "orders": [
    {
      "id": 1001,
      "status": "shipped",
      "total": 59.9,
      "customer": {
        "name": "Ana Ruiz",
        "country": "ES"
      },
      "items": [
        "SKU-104",
        "SKU-221"
      ]
    },
    {
      "id": 1002,
      "status": "pending",
      "total": 18.5,
      "customer": {
        "name": "Jonas Berg",
        "country": "SE"
      },
      "items": [
        "SKU-310"
      ]
    },
    {
      "id": 1003,
      "status": "shipped",
      "total": 112,
      "customer": {
        "name": "Mei Tanaka",
        "country": "JP"
      },
      "items": [
        "SKU-104",
        "SKU-415",
        "SKU-502"
      ]
    }
  ]
}

orders {
  id: 1001
  status: "shipped"
  total: 59.9
  customer {
    name: "Ana Ruiz"
    country: "ES"
  }
  items: "SKU-104"
  items: "SKU-221"
}
orders {
  id: 1002
  status: "pending"
  total: 18.5
  customer {
    name: "Jonas Berg"
    country: "SE"
  }
  items: "SKU-310"
}
orders {
  id: 1003
  status: "shipped"
  total: 112
  customer {
    name: "Mei Tanaka"
    country: "JP"
  }
  items: "SKU-104"
  items: "SKU-415"
  items: "SKU-502"
}

Protobuf output is 34% smaller than the JSON input. The same data is 375 characters as minified JSON and 689 as pretty-printed JSON. Sizes are character counts, not tokens: token counts depend on the model's tokenizer (see the tokenizer comparison).

JSON to Protobuf: what changes

• Nested objects become message blocks and arrays become repeated fields. The result is text format, which protoc can parse with --encode only if you provide a .proto file that declares these fields.
• Reading JSON: Input must be strict JSON: no comments, trailing commas, or single quotes. If it came from an LLM or a log file, run it through the JSON repair tool first.
• Writing Protobuf: Output is Protobuf text format: arrays become repeated fields and nested objects become message blocks. To encode binary Protobuf you still need a .proto schema with matching field names and types, and keys like @_id or opt-level are not valid field names.

Why Convert JSON to Protobuf?

Use Protobuf for high-performance internal APIs, microservices communication, or when you need maximum efficiency and have defined schemas.