# Pre-Populating Existing Customer Data

Engine Partner Pages support the ability to add certain tags with varying use cases, which are outlined in this section.

### Client Tag Use Cases

* Prefilling Customer Data
  * Decreases friction in the user experience and increases application submission rates
  * Useful when you already have that info on hand for that user, or want the front-end to default to particular values
* [Channel Partner Reporting](/developer-center/channel-partner-reporting/engine-analytics-api.md)

### How to Implement Client Tags for Reporting & Customer Data Prefill

To **add client tags** to a Partner Page integration for the purpose of enhanced reporting, add query string parameters to the respective URL in the following format\*:

```
?tag.key_1=value_1&tag.key_2=value_2
```

To **prefill customer data fields** in a Partner Page for the purpose of decreased friction in user experience, add query string parameters to the respective URL in the following format\*:

```
?app.key_1=value_1&app.key_2=value_2
```

{% hint style="info" %}
\*The first query parameter appended at the end of a URL/path should start with a question mark `?`; all subsequent parameters should start with an ampersand `&`.
{% endhint %}

#### Sample Partner Page URL

```html
https://moneylion.com/network/{channel}/{zone}/search?app.loanAmount=10000&tag.clientId=1234
```

<mark style="color:$primary;">In the above example,</mark> <mark style="color:$primary;">`clientId`</mark> <mark style="color:$primary;">is available as a tag for reporting purposes and the partner page "loan amount" field will be prepopulated with the value of "$</mark>10,000" for the consumer <mark style="color:$primary;">when the page is rendered.</mark>

### Supported Client Tag Keys (for any integration type)

These are the keys that are currently fully supported across all Engine partner page types. Please note that the keys below are case-sensitive:

* agentId
* campaignId
* clientId
* deviceid
* medium
* sourceId
* subid
* subid1
* subid2
* subid3
* target
* trafficsource
* userid

If a different key is needed, please reach out to your Partner Manager - we *may* be able to accommodate, but adding nonstandard keys will increase the time it takes Engine to report Client Tag values back to you and is therefore not recommended.


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