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JSON-Cadence Data Interchange Format

Version 0.1.3

JSON-Cadence is a data interchange format used to represent Cadence values as language-independent JSON objects.

This format includes less type information than a complete ABI, and instead promotes the following tenets:

  • Human-readability - JSON-Cadence is easy to read and comprehend, which speeds up development and debugging.
  • Compatibility - JSON is a common format with built-in support in most high-level programming languages, making it easy to parse on a variety of platforms.
  • Portability - JSON-Cadence is self-describing and thus can be transported and decoded without accompanying type definitions (i.e. an ABI).

Table of Contents

Void

{
  "type": "Void"
}

Example

{
  "type": "Void"
}

Optional

{
  "type": "Optional",
  "value": null | <value>
}

Example

// Non-nil

{
  "type": "Optional",
  "value": {
    "type": "UInt8",
    "value": "123"
  }
}

// Nil

{
  "type": "Optional",
  "value": null
}

Bool

{
  "type": "Bool",
  "value": true | false
}

Example

{
  "type": "Bool",
  "value": true
}

String

{
  "type": "String",
  "value": "..."
}

Example

{
  "type": "String",
  "value": "Hello, world!"
}

Address

{
  "type": "Address",
  "value": "0x0" // as hex-encoded string with 0x prefix
}

Example

{
  "type": "Address",
  "value": "0x1234"
}

Integers

[U]Int, [U]Int8, [U]Int16, [U]Int32,[U]Int64,[U]Int128, [U]Int256, Word8, Word16, Word32, or Word64

Although JSON supports integer literals up to 64 bits, all integer types are encoded as strings for consistency.

While the static type is not strictly required for decoding, it is provided to inform client of potential range.

{
  "type": "<type>",
  "value": "<decimal string representation of integer>"
}

Example

{
  "type": "UInt8",
  "value": "123"
}

Fixed Point Numbers

[U]Fix64

Although fixed point numbers are implemented as integers, JSON-Cadence uses a decimal string representation for readability.

{
    "type": "[U]Fix64",
    "value": "<integer>.<fractional>"
}

Example


{
    "type": "Fix64",
    "value": "12.3"
}

Array

{
  "type": "Array",
  "value": [
    <value for index 0>,
    <value for index 1>
    ...
  ]
}

Example

{
  "type": "Array",
  "value": [
    {
      "type": "Int16",
      "value": "123"
    },
    {
      "type": "String",
      "value": "test"
    },
    {
      "type": "Bool",
      "value": true
    }
  ]
}

Dictionary

Dictionaries are encoded as a list of key-value pairs to preserve the deterministic ordering implemented by Cadence.

{
  "type": "Dictionary"
  "value": [
    {
      "key": "<key>", 
      "value": <value>
    },
    ...
  ]
}

Example

{
  "type": "Dictionary"
  "value": [
    {
      "key": {
        "type": "UInt8",
        "value": "123"
      }, 
      "value": {
        "type": "String",
        "value": "test"
      },
    }
  ],
  ...
}

Composites (Struct, Resource, Event)

Event, Struct, Resource

Composite fields are encoded as a list of name-value pairs in the order in which they appear in the composite type declaration.

{
  "type": "Struct" | "Resource" | "Event",
  "value": {
    "id": "<fully qualified type identifier>",
    "fields": [
      {
        "name": "<field name>",
        "value": <field value>
      },
      ...
    ]
  }
}

Example

{
  "type": "Resource",
  "value": {
    "id": "0x3.GreatContract.GreatNFT",
    "fields": [
      {
        "name": "power",
        "value": {"type": "Int", "value": "1"}
      }
    ]
  }
}