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## Resource: Introduction

## Article: Introduction

## Article Link: https://dev.wix.com/docs/api-reference/crm/members-contacts/contacts/extended-fields/introduction.md

## Article Content:

# About the Extended Fields API

The Extended Fields API provides functionality for managing extended field definitions, allowing you to retrieve and store specific contact information relevant to a site. Basic fields such as name, address, email, and phone number are stored in a contact's default fields, while additional information about a contact can be stored in extended fields. For example, you can create an extended field named "Nickname" to store a contact's nickname. 

With the Extended Fields API, you can: 
- Create, manage, and delete extended fields.
- Retrieve existing extended fields. 

Learn more about [Adding and Managing Custom Contact Fields](https://support.wix.com/en/article/adding-custom-fields-to-contacts).

## Before you begin

It's important to note the following points before starting to code:
- When you create a new extended field, it's available for use for all contacts,
and the field is blank by default.
- Extended field keys can't be changed once created. 
- When you delete an extended field, you also remove its associated values from any contact that uses the field. 
- Possible data types for extended fields include:
  - Text
  - Number
  - Date
  - URL
- Each extended field is represented as a key-value pair in the contact object in `info.extendedFields`. To manage the extended fields of an individual contact, use the [Contacts API](https://dev.wix.com/docs/rest/crm/members-contacts/contacts/contacts/introduction.md). Each key is the extended field key, and each value is the field's value for a contact. Empty extended fields are not returned in contact objects.

## Terminology
- **Extended field:** A customized field that can store additional information for a contact. A contact’s extended field data is available in `info.extendedFields` of the `contact` object. There are 2 types of extended fields:
  - **System field:** An extended field created by apps built by Wix, such as Wix Stores or Wix Members, to enrich contact data. These fields can't be renamed and are typically read-only.
  - **Custom field:** An extended field created by calling the Find Or Create Extended Field method. Custom fields can be renamed. 

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