> ## Documentation Index
> Fetch the complete documentation index at: https://spreecommerce.org/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Create a product custom field

> Sets a custom field value on the product. Requires an existing CustomFieldDefinition; pass its prefixed `cfdef_…` id.

**Required scope:** `write_products` (for API-key authentication).



## OpenAPI

````yaml /api-reference/admin.yaml post /api/v3/admin/products/{product_id}/custom_fields
openapi: 3.0.3
info:
  title: Admin API
  contact:
    name: Spree Commerce
    url: https://spreecommerce.org
    email: hello@spreecommerce.org
  description: >
    Spree Admin API v3 - Administrative API for managing products, orders, and
    store settings.


    ## Authentication


    The Admin API requires a secret API key passed in the `x-spree-api-key`
    header.

    Secret API keys can be generated in the Spree admin dashboard.


    ## Response Format


    All responses are JSON. List endpoints return paginated responses with
    `data` and `meta` keys.

    Single resource endpoints return a flat JSON object.


    ## Resource IDs


    Every resource is identified by an opaque string ID (e.g. `prod_86Rf07xd4z`,

    `variant_k5nR8xLq`, `or_UkLWZg9DAJ`). Use these IDs everywhere — URL paths,

    request bodies, and Ransack filters all accept them directly.


    ## Error Handling


    Errors return a consistent format:

    ```json

    {
      "error": {
        "code": "validation_error",
        "message": "Validation failed",
        "details": { "name": ["can't be blank"] }
      }
    }

    ```
  version: v3
servers:
  - url: http://{defaultHost}
    variables:
      defaultHost:
        default: localhost:3000
security: []
tags:
  - name: Authentication
    description: Admin user authentication
  - name: Product Catalog
    description: Products, variants, and option types
  - name: Orders
    description: >-
      Order management — orders, items, payments, fulfillments, refunds, gift
      cards, store credits
  - name: Customers
    description: Customer management — profiles, addresses, store credits, credit cards
  - name: Configuration
    description: Store configuration — payment methods, tag autocomplete
paths:
  /api/v3/admin/products/{product_id}/custom_fields:
    post:
      tags:
        - Products
      summary: Create a product custom field
      description: >-
        Sets a custom field value on the product. Requires an existing
        CustomFieldDefinition; pass its prefixed `cfdef_…` id.


        **Required scope:** `write_products` (for API-key authentication).
      parameters:
        - name: x-spree-api-key
          in: header
          required: true
          schema:
            type: string
        - name: Authorization
          in: header
          required: true
          schema:
            type: string
        - name: product_id
          in: path
          required: true
          schema:
            type: string
      requestBody:
        content:
          application/json:
            schema:
              type: object
              required:
                - custom_field_definition_id
                - value
              properties:
                custom_field_definition_id:
                  type: string
                  description: Prefixed `cfdef_…` id
                value:
                  description: Value matching the definition's `field_type`
      responses:
        '201':
          description: custom field created
          content:
            application/json:
              example:
                id: cf_gbHJdmfrXB
                label: Description
                type: Spree::Metafields::LongText
                field_type: long_text
                key: custom.description
                value: A longer description
                created_at: '2026-05-17T22:58:11.733Z'
                updated_at: '2026-05-17T22:58:11.733Z'
                storefront_visible: true
                custom_field_definition_id: cfdef_gbHJdmfrXB
        '422':
          description: duplicate definition for the same product
          content:
            application/json:
              example:
                error:
                  code: validation_error
                  message: Metafield definition has already been taken
                  details:
                    metafield_definition_id:
                      - has already been taken
      security:
        - api_key: []
          bearer_auth: []
      x-codeSamples:
        - lang: javascript
          label: Spree Admin SDK
          source: >-
            import { createAdminClient } from '@spree/admin-sdk'


            const client = createAdminClient({
              baseUrl: 'https://your-store.com',
              secretKey: 'sk_xxx',
            })


            const customField = await
            client.products.customFields.create('prod_UkLWZg9DAJ', {
              custom_field_definition_id: 'cfdef_AbC123XyZ',
              value: 'wool',
            })
components:
  securitySchemes:
    api_key:
      type: apiKey
      name: x-spree-api-key
      in: header
      description: Secret API key for admin access
    bearer_auth:
      type: http
      scheme: bearer
      bearerFormat: JWT
      description: JWT token for admin user authentication

````