> For the complete documentation index, see [llms.txt](https://documentation.crossengage.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://documentation.crossengage.io/data-and-engagement-platform/data-management/data-management-with-data-feeds/users.md).

# Users

The CrossEngage Platform stores User Data, such that each User can be identified by their Email Address and Business Unit, or External ID (**ID**). This is important, so that Orders and Events can be linked to individual users.

### General limitations:

When creating or importing Users, please adhere to the following limitations:

* String fields **cannot** be bigger than **16 KB**. To transmit more data, please send it as an array of strings, or numbers (or other primitive types).
* The maximum size of a JSON-User object **cannot** exceed **1 MB**.
* There is a limitation of **30** nested fields for one CrossEngage instance.
* Nesting deeper than **two** levels is not possible.
* The **maximum** number of json objects that a single document/customer can contain across all fields and nested types is **1000.** This limit helps to prevent out of memory errors when a document contains too many nested objects.