# User Identifier

A User Identifier is a value used to identify each individual user — and it is critically important.

All features provided by Hackle are behavior-based.\
Therefore, to accurately analyze user behavior, the criteria for identifying a **user** must be clearly defined.

Being able to clearly identify a specific user allows you to accurately calculate goals such as revenue per user, search conversion rate, and product page views — based on that user's history of purchases, searches, and product views.

{% hint style="info" %}
An identifier must be a unique value with no duplicates.\
For example, a member ID or a device ID that can uniquely identify a user.
{% endhint %}

### Basic User Identifiers

While you can send various user identifiers to Hackle, the most fundamental ones are User ID and Device ID.

<table><thead><tr><th width="146.5703125">Identifier</th><th>Description</th></tr></thead><tbody><tr><td><strong>DeviceID</strong></td><td>The unique identifier for the device (phone, PC, tablet) used to access the service.<br>It remains the same regardless of whether a UserID is set.</td></tr><tr><td><strong>HackleDeviceId</strong></td><td>If no Device ID is separately configured, this value is used as the DeviceID.</td></tr><tr><td><strong>UserID</strong></td><td>A member ID that uniquely identifies a user within the service.<br>It is recommended to set this to the ID generated after the user logs in or registers.</td></tr><tr><td><strong>HackleID</strong></td><td>The <a href="/pages/QowaBg651RXYlAnKd18I">Hackle ID</a> provided by Hackle.<br>When both User ID and Device ID are sent, a Hackle ID is generated by combining the two — enabling more accurate identification of the same user.</td></tr><tr><td>SessionID</td><td>The <a href="/pages/LmFaGj340F0iSsnhNsJo">Session ID</a> maintained during a user's continuous activity.</td></tr><tr><td><strong>ID</strong><br>(deprecated)</td><td>An identifier previously used as the default identifier.<br>Send whichever of Device ID or User ID can be consistently sent as the same value from both the frontend and server.<br>For frontend SDKs, if no separate configuration is made, the Device ID value is sent as-is for ID. This means ID, Device ID, and Hackle Device ID all hold the same value.</td></tr></tbody></table>

### Additional User Identifiers

In addition to the default user identifiers, you can send identifiers of the 'Custom' type.

#### Custom Type

These are user identifiers you define yourself to fit your service.\
For example, in a commerce context, you might use Session ID or order number. Note that Custom type identifiers cannot use the Hackle ID.

{% hint style="danger" %}
Important notes when using Advertising IDs (GAID, IDFA)

When collecting these IDs, you must strictly follow Google's and Apple's policies. Please refer to the links below for each company's policies.

* [Google Advertising ID usage guidelines](https://developer.android.com/training/articles/user-data-ids?hl=ko#advertising-ids)
* [Apple's User Privacy and Data Use guidelines](https://developer.apple.com/kr/app-store/user-privacy-and-data-use/)
  {% endhint %}


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