> For the complete documentation index, see [llms.txt](https://doc.wearepatchworks.com/product-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doc.wearepatchworks.com/product-documentation/process-flows/cross-reference-lookups/adding-a-cross-reference-lookup.md).

# Adding a cross-reference lookup

## Introduction

If you have your own set of data values that you want to cross-reference, you can add your own **cross-reference lookup**. Once added, you can [use it in field mapping transformations](/product-documentation/process-flows/cross-reference-lookups/using-a-cross-reference-lookup-in-field-transformations.md).

{% hint style="info" %}
If required, cross-reference lookups can also be updated via the Patchworks API. For more information please see our [Cross-reference lookup API ](/product-documentation/developer-hub/patchworks-core-api/core-api-spotlights/working-with-cross-reference-lookup-api-requests.md)section.
{% endhint %}

## The steps

**Step 1**\
Log into the Patchworks dashboard, then select **process flows** <mark style="color:orange;">\~</mark> **cross-reference lookups** from the left-hand navigation bar.

**Step 2**\
Click the **create cross-reference lookup** button:

<figure><img src="/files/BUVNBYd6qntDP89ZCYNe" alt=""><figcaption></figcaption></figure>

**Step 3**\
Enter basic details for this lookup:

<figure><img src="/files/yRZyVvDga0Yd86G0ePkJ" alt=""><figcaption></figcaption></figure>

| Field       | Summary                                                                                                                                                                                                                                                                                |
| ----------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Name        | Enter a name by which this lookup will be identified throughout Patchworks. Special characters are allowed.                                                                                                                                                                            |
| Description | Provide a bit more detail to help users understand what this lookup includes. Special characters are allowed.                                                                                                                                                                          |
| Default     | Set a fallback value to be used when this lookup is [used for field transformations ](/product-documentation/process-flows/cross-reference-lookups/accessing-cross-reference-lookups.md)and the associated field has a value that can't be found in the set of values for this lookup. |

**Step 4**\
Click the **create** button to confirm these details. The new lookup is created and you're ready to add your required values.

**Step 5**\
Click the **create value** button:

<div align="left"><figure><img src="/files/XA1yhZzuPqUayCyuCsuB" alt=""><figcaption></figcaption></figure></div>

**Step 6**\
Enter details for your first value:

<figure><img src="/files/vvnqfc1Qwm5hwWgnqHJI" alt=""><figcaption></figcaption></figure>

| Field | Summary                                                                      |
| ----- | ---------------------------------------------------------------------------- |
| Left  | Enter the 'left side' of the value mapping - i.e. the value to be converted. |
| Right | Enter the 'right side' of the value mapping - i.e. the converted value.      |

{% hint style="info" %}
You can include special characters when defining lookup values. Values do NOT need to be unique.
{% endhint %}

**Step 7**\
Click the **create** button to save this entry.

**Step 8**\
Add more values as needed.