# Custom Properties

Extension mechanism for arbitrary key-value metadata not covered by the standard.

## Custom Properties {#custom-properties}

type: CustomProperties

A list of key/value pairs for custom properties.
Implemented as array of type [CustomProperty](#custom-property)[].

## Custom Property {#custom-property}

type: CustomProperty

| Property | Type | Required | Description |
|---|---|---|---|
| `property` | string | No | The name of the key. Names should be in camel case–the same as if they were permanent properties in the contract. |
| `value` | [AnyType](/docs/reference/data-contract/common-types/#any-type) | No | The value of the key. |