# SKU lists

SKU lists are used to group more [SKUs](/core-api-reference/skus.md), either automatically (i.e. through a RegEx — max **5000** chars allowed) or manually (i.e. by creating and sorting more [SKU list items](/core-api-reference/sku_list_items.md)).

{% hint style="info" %}
SKU lists cannot contain [bundles](/core-api-reference/bundles.md). If a bundle is associated with an SKU list, they are considered matching resources, which is meaningful for the scope of specific [promotions](/core-api-reference/free_gift_promotions.md) and [promotion rules](/core-api-reference/promotion_rules.md) application.
{% endhint %}

{% hint style="warning" %}
SKU uniqueness is not enforced on SKU list. That means an SKU list can contain the same SKU multiple times.
{% endhint %}

<details>

<summary>Data model</summary>

Check the related [ER diagram](https://commercelayer.io/docs/data-model/sku-lists) and explore the flowchart that illustrates how the SKU list resource relates to the other API entities.

</details>


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