# Creating a Custom Field

A custom field lets you map fields specific to your organization. These fields could include custom fields, tags, or metadata that don't have a standard Aisera equivalent. To create a custom field, navigate to **Settings > Data Sources** in the Aisera Admin UI and select the Data Source you would like to create a custom field for. Click **New Custom Field** at the bottom of the **Data Source Details** page to open the **New Custom Field** window. 

### Field Name

This field intake the internal name for the custom field. This name must:

* Not contain dots
* Not match a field name already used internally by the Aisera platform
* Be unique within the Data Source

{% hint style="success" %}
It is best practice to name custom fields with a unique name followed by an underscore, such as `mycompany_`. This makes custom fields easy to distinguish from standard Aisera fields and easy to locate if a platform upgrade requires manual updates.
{% endhint %}

### Display Name

A human readable label. When this is set, the name will be shown alongside the field name in the mappings list.

### Content Type

Determines which content type the field applies to. Only appears when the selected content type has subtypes. Defaults to the content type you are currently working with.

### Value Generation Type

Controls how the fields value is populate. Select one of the following:

* **Field Mapping** - Maps directly to a field in the Data Source. Insert the corresponding  field name or [JSONPath expression](https://www.rfc-editor.org/rfc/rfc9535) in the \<Application Name> Field that appears.
* **Derivation Rule** - Populates the field using one or more derivation rules. Click **Add a Derivation Rule** to open the [New Derivation Rule](https://docs.aisera.com/aisera-platform/adding-data-to-your-tenant/data-ingestion/field-mappings/derivation-rules) window.

### Outbound Field

The [JSONPath expression](https://www.rfc-editor.org/rfc/rfc9535) for the path in the external system to write data back to. When the Aisera Platform sends data to the external system, it will use this path instead of the **\<Application Name> Field** path. If left empty, the **\<Application Name> field** path is used for both reading and writing.

### Anonymization Rule

An optional JSON configuration defining how Personally Identifiable Information (PII) in this field's values should be detected and anonymized during ingestion. The Aisera Platform uses Microsoft Presidio anonymization ending. See the [Presidio Anonymizer documentation](https://microsoft.github.io/presidio/anonymizer/) for configuration details.