---
schema_version: "1"
id: 891a530b53d42671de4d45b894e0badcf7ce79a49d3ac088355233d1faaeb088
title: Customer Key
collection: developer
version: current
locale: en-us
portal_url: https://docs.salesforce.com/developer/current/en-us/marketing-cloud/guides/mc-apis/customer_key.md
canonical_url: https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/customer_key.html
source_site: developer.salesforce.com
content_type: documentation
content_hash: 0b5d3144ce9c590612021d3a4304a72a8e077a28536a2903fb5fbba00fc1076c
products:
  - Marketing Cloud Engagement APIs and Programmatic Languages
  - Marketing Cloud
---
# Customer Key

A customer key is a user-defined identifier for an asset. Each customer key is a unique value across your enterprise. The customer key isn’t a required field, and if you don’t provide a value, Marketing Cloud Engagement generates a unique GUID value for the customer key.

Add a customer key to the asset as a string with a 36-character limit, using the `customerKey` attribute.

## Sample Asset with Customer Key

```json
{
  "name": "NTO Welcome Series Email",
  "assetType": {
    "id": 207,
    "name": "templatebasedemail"
  },
  "customerKey": "090c69e7-59ac-4286-8733-f8f76example"
}
```

## Related Items

- [Asset Model](https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/asset-model.md)
- [Asset Model Example](https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/asset_model_examples.md)