> For the complete documentation index, see [llms.txt](https://help.mimeeq.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.mimeeq.com/api/custom-fields.md).

# Custom Fields

Define additional fields for option-set options, cart submissions and product data-grid (bill of materials) items. A field definition describes the field’s key, label, data type, validation and display configuration; it is not the value entered on an individual record.

Use this section to discover existing fields or configure the metadata an integration needs. For example, define an internal reference on an option or an additional field on a cart submission.

### What you can do

| Task                         | Reference                                                                                   |
| ---------------------------- | ------------------------------------------------------------------------------------------- |
| Find available custom fields | [List Custom Fields](https://help.mimeeq.com/developers/custom-fields/list-custom-fields)   |
| Add a new custom field       | [Create Custom Field](https://help.mimeeq.com/developers/custom-fields/create-custom-field) |
| Read one custom field        | [Get Custom Field](https://help.mimeeq.com/developers/custom-fields/get-custom-field)       |
| Change custom field          | [Update Custom Field](https://help.mimeeq.com/developers/custom-fields/update-custom-field) |
| Remove custom field          | [Delete Custom Field](https://help.mimeeq.com/developers/custom-fields/delete-custom-field) |

### Before you start

Your API key needs `customFields:read` to read these resources. Use `customFields:write` for write operations.

### Important behaviour

Choose `resourceType` on every request: `OPTION_SET`, CART or `PRODUCT_DATA_GRID`. The same field ID must be interpreted in its resource context. Lists include `SYSTEM` and `CUSTOM` definitions; system definitions cannot be changed. Updates replace the definition, so preserve every setting you want to keep. Deleting a definition is a schema change; do not assume it edits existing record values.


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