extensionCustomFunctions object

{
  "functions": [
    {
      "id": "{string}",
      "name": "{string}",
      "description": "{string}",
      "helpUrl": "{string}",
      "parameters": [
        {
          extensionFunctionParameter object
        }
      ],
      "result": {
        extensionResult object
      },
      "stream": {boolean},
      "volatile": {boolean},
      "cancelable": {boolean},
      "requiresAddress": {boolean},
      "requiresParameterAddress": {boolean}
    }
  ],
  "namespace": {
    "id": "{string}",
    "name": "{string}"
  },
  "allowCustomDataForDataTypeAny": {boolean}
}

{
  "type": "object",
  "description": "Custom function enable developers to add new functions to Excel by defining those functions in JavaScript as part of an add-in. Users within Excel can access custom functions just as they would any native function in Excel, such as SUM().",
  "properties": {
    "functions": {
      "description": "Array of function object which defines function metadata.",
      "items": {
        "$ref": "#/definitions/extensionFunction"
      },
      "maxItems": 20000,
      "minItems": 1,
      "type": "array"
    },
    "namespace": {
      "$ref": "#/definitions/extensionCustomFunctionsNamespace"
    },
    "allowCustomDataForDataTypeAny": {
      "type": "boolean",
      "description": "Allows a custom function to accept Excel data types as parameters and return values.",
      "default": false
    }
  },
  "required": [
    "functions",
    "namespace"
  ]
}