# Create a metafield definition

> Declare a new custom field on an owner type.

`POST /rest/api/metafield_definitions`

Creates a MetafieldDefinition resource.

Declares a custom field. Give it a `namespace` and `key` (which together identify it), the `ownerType` it applies to, the `type` of data it holds, and optionally `validations`. Once created, you can set [Metafield](/api/product-management/metafields/) values for it on records of that owner type.

## Headers

| Name                         | Type     | Required | Description                                                                                                                                      |
| ---------------------------- | -------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |
| `X-Flowkiwi-Organization-Id` | `string` | Yes      | The organization the request acts as. Determines the identity, permissions and ownership applied when reading or modifying data on the instance. |

## Request body

| Property      | Type                                              | Required | Description                                                                                         |
| ------------- | ------------------------------------------------- | -------- | --------------------------------------------------------------------------------------------------- |
| `name`        | `string`                                          | -        |                                                                                                     |
| `description` | `string \| null`                                  | -        |                                                                                                     |
| `namespace`   | `string`                                          | -        |                                                                                                     |
| `key`         | `string`                                          | -        |                                                                                                     |
| `ownerType`   | `string`                                          | Yes      |                                                                                                     |
| `type`        | `string`                                          | Yes      |                                                                                                     |
| `validations` | `EmbeddedMetafieldDefinitionValidationResource[]` | -        | The validation rules applied to the values of metafields using this definition.                     |
| `constraints` | `EmbeddedMetafieldDefinitionConstraintResource[]` | -        | The constraint rules scoping where this metafield definition applies (e.g. by category or channel). |

## Response

**201** - MetafieldDefinition resource created

| Property          | Type                                              | Required | Description                                                                                         |
| ----------------- | ------------------------------------------------- | -------- | --------------------------------------------------------------------------------------------------- |
| `@context`        | `object`                                          | -        |                                                                                                     |
| `@id`             | `string`                                          | Yes      |                                                                                                     |
| `@type`           | `string`                                          | Yes      |                                                                                                     |
| `id`              | `string`                                          | -        | The resource's unique identifier (UUID).                                                            |
| `name`            | `string`                                          | -        | The human-readable name of the metafield definition.                                                |
| `description`     | `string \| null`                                  | -        | The description of the metafield definition.                                                        |
| `namespace`       | `string`                                          | -        | The container for a group of metafields that the metafield definition is associated with.           |
| `key`             | `string`                                          | -        | The unique identifier for the metafield definition within its namespace.                            |
| `ownerType`       | `string`                                          | Yes      | The resource type that the metafield definition is attached to.                                     |
| `type`            | `string`                                          | Yes      | The type of data that each of the metafields that belong to the metafield definition will store.    |
| `createdAt`       | `string`                                          | -        | The date and time when the resource was created (ISO 8601 format).                                  |
| `updatedAt`       | `string`                                          | -        | The date and time when the resource was last modified (ISO 8601 format).                            |
| `validations`     | `EmbeddedMetafieldDefinitionValidationResource[]` | -        | The validation rules applied to the values of metafields using this definition.                     |
| `constraints`     | `EmbeddedMetafieldDefinitionConstraintResource[]` | -        | The constraint rules scoping where this metafield definition applies (e.g. by category or channel). |
| `metafieldsCount` | `integer`                                         | -        | The count of the metafields that belong to the metafield definition.                                |

## Errors

**400** - Invalid input

| Property   | Type             | Required | Description                                                                                                                          |
| ---------- | ---------------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------ |
| `@context` | `object`         | -        |                                                                                                                                      |
| `@id`      | `string`         | Yes      |                                                                                                                                      |
| `@type`    | `string`         | Yes      |                                                                                                                                      |
| `title`    | `string \| null` | -        | A short, human-readable summary of the problem.                                                                                      |
| `detail`   | `string \| null` | -        | A human-readable explanation specific to this occurrence of the problem.                                                             |
| `status`   | `number \| null` | -        |                                                                                                                                      |
| `instance` | `string \| null` | -        | A URI reference that identifies the specific occurrence of the problem. It may or may not yield further information if dereferenced. |
| `type`     | `string`         | -        | A URI reference that identifies the problem type                                                                                     |

**403** - Access denied. The caller is missing one or more identity permissions required for this operation.

| Property             | Type       | Required | Description                                                                                                                                |
| -------------------- | ---------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------ |
| `@context`           | `object`   | -        |                                                                                                                                            |
| `@id`                | `string`   | Yes      |                                                                                                                                            |
| `@type`              | `string`   | Yes      |                                                                                                                                            |
| `type`               | `string`   | -        |                                                                                                                                            |
| `title`              | `string`   | -        |                                                                                                                                            |
| `status`             | `integer`  | -        |                                                                                                                                            |
| `detail`             | `string`   | -        |                                                                                                                                            |
| `missingPermissions` | `string[]` | -        | Identity permissions that the caller is missing for this operation. Present only when the 403 is caused by a denied identity:* permission. |

**422** - An error occurred

| Property     | Type             | Required | Description |
| ------------ | ---------------- | -------- | ----------- |
| `@context`   | `object`         | -        |             |
| `@id`        | `string`         | Yes      |             |
| `@type`      | `string`         | Yes      |             |
| `status`     | `integer`        | -        |             |
| `violations` | `object[]`       | -        |             |
| `detail`     | `string`         | -        |             |
| `type`       | `string`         | -        |             |
| `title`      | `string \| null` | -        |             |
| `instance`   | `string \| null` | -        |             |

## Examples

### Example request

```bash
curl -X POST 'https://<tenant>.product-management.flowkiwi.net/rest/api/metafield_definitions' \
  -H 'Authorization: Bearer {token}' \
  -H 'X-Flowkiwi-Organization-Id: <org_id>' \
  -H 'Accept: application/ld+json' \
  -H 'Content-Type: application/ld+json' \
  -d '{
  "name": "Care instructions",
  "description": "Washing and care guidance shown on the product page.",
  "namespace": "custom",
  "key": "care_instructions",
  "ownerType": "/rest/api/metafield_owner_types/products",
  "type": "/rest/api/metafield_definition_types/multi_line_text_field",
  "constraints": [
    {
      "key": "/rest/api/metafield_definition_constraint_types/category",
      "values": [
        "019af8a0-1111-7222-8333-444455556666",
        "019af8a0-7777-7888-8999-aaaabbbbcccc"
      ]
    }
  ]
}'
```

### Example response

```json
{
  "@context": "/contexts/MetafieldDefinition",
  "@id": "/rest/api/metafield_definitions/019afb05-5e6f-7081-8a92-4d5e6f708192",
  "@type": "MetafieldDefinition",
  "id": "019afb05-5e6f-7081-8a92-4d5e6f708192",
  "name": "Care instructions",
  "description": "Washing and care guidance shown on the product page.",
  "namespace": "custom",
  "key": "care_instructions",
  "ownerType": "/rest/api/metafield_owner_types/products",
  "type": "/rest/api/metafield_definition_types/multi_line_text_field",
  "validations": [],
  "constraints": [
    {
      "key": "/rest/api/metafield_definition_constraint_types/category",
      "values": [
        "019af8a0-1111-7222-8333-444455556666",
        "019af8a0-7777-7888-8999-aaaabbbbcccc"
      ]
    }
  ],
  "metafieldsCount": 0,
  "createdAt": "2026-01-15T09:30:00+00:00",
  "updatedAt": "2026-01-15T09:30:00+00:00"
}
```