> ## Documentation Index
> Fetch the complete documentation index at: https://terminal49.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Update a custom field definition

> Update a custom field definition in the Terminal49 API, including its display label, data type constraints, and enum option set for shipments or containers.

Update an existing custom field definition.

## Path parameters

| Parameter | Description                                          |
| --------- | ---------------------------------------------------- |
| `id`      | The unique identifier of the custom field definition |

## Request body

Provide the fields you want to update, such as `display_name`, `description`, `validation`, or `default_format`.

## Notes

You cannot change `api_slug`, `entity_type`, or `data_type` after creation.


## OpenAPI

````yaml patch /custom_field_definitions/{id}
openapi: 3.0.0
info:
  title: Terminal49 API Reference
  version: 0.2.0
  contact:
    name: Terminal49 API support
    url: https://www.terminal49.com
    email: support@terminal49.com
  description: >-
    The Terminal 49 API offers a convenient way to programmatically track your
    shipments from origin to destination.


    Please enter your API key into the "Variables" tab before using these
    endpoints within Postman.
  x-label: Beta
  termsOfService: https://www.terminal49.com/terms
servers:
  - url: https://api.terminal49.com/v2
    description: Production
security:
  - authorization: []
tags:
  - name: Containers
  - name: Custom Field Definitions
  - name: Custom Field Options
  - name: Custom Fields
  - name: Shipments
  - name: Locations
  - name: Events
  - name: Tracking Requests
  - name: Webhooks
  - name: Webhook Notifications
  - name: Ports
  - name: Metro Areas
  - name: Terminals
  - name: Routing (Paid)
  - name: Documents
  - name: Email Submissions
  - name: Document Schemas
  - name: Search
paths:
  /custom_field_definitions/{id}:
    parameters:
      - schema:
          type: string
        name: id
        in: path
        required: true
        description: Custom field definition ID
    patch:
      tags:
        - Custom Field Definitions
      summary: Update a custom field definition
      operationId: patch-custom-field-definitions-id
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                data:
                  type: object
                  required:
                    - type
                    - attributes
                  properties:
                    type:
                      type: string
                      enum:
                        - custom_field_definition
                    attributes:
                      type: object
                      properties:
                        display_name:
                          type: string
                        description:
                          type: string
                          nullable: true
                        validation:
                          type: object
                          nullable: true
                          additionalProperties: true
                        default_format:
                          type: string
                          nullable: true
                        default_value:
                          $ref: '#/components/schemas/custom_field_value'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: object
                properties:
                  data:
                    $ref: '#/components/schemas/custom_field_definition'
                  links:
                    $ref: '#/components/schemas/link-self'
components:
  schemas:
    custom_field_value:
      description: Raw custom field value (type depends on definition)
      nullable: true
      oneOf:
        - type: string
        - type: number
        - type: boolean
        - type: array
          items:
            type: string
        - type: object
    custom_field_definition:
      title: Custom field definition
      type: object
      properties:
        id:
          type: string
          format: uuid
        type:
          type: string
          enum:
            - custom_field_definition
        attributes:
          type: object
          properties:
            entity_type:
              type: string
              enum:
                - Shipment
                - Container
                - TrackingRequest
            api_slug:
              type: string
            display_name:
              type: string
            description:
              type: string
              nullable: true
            data_type:
              type: string
              enum:
                - short_text
                - number
                - date
                - datetime
                - boolean
                - enum
                - enum_multi
                - reference
            reference_type:
              type: string
              nullable: true
            validation:
              type: object
              nullable: true
              additionalProperties: true
            default_format:
              type: string
              nullable: true
            default_value:
              $ref: '#/components/schemas/custom_field_value'
          required:
            - entity_type
            - api_slug
            - display_name
            - data_type
      required:
        - id
        - type
    link-self:
      title: link
      type: object
      properties:
        self:
          type: string
          format: uri
  securitySchemes:
    authorization:
      name: Authorization
      type: apiKey
      in: header
      description: >-
        Use a Terminal49 API key in the `Authorization` header with the `Token`
        prefix.


        `Authorization: Token YOUR_API_KEY`

````