# Extension Data (Advanced)

Learn how to attach custom data to events.

## What is Extension Data?

Extension Data is a feature that allows you to attach additional data to user interaction events. This data will be passed along to your tag manager integrations.

## How to use Extension Data?

> **PII Notice**
>
> Extension data will end up in your tag manager integrations. You must ensure
> that no Personally identifiable information (PII) is passed in as extension
> data.

There are a number of ways to use Extension Data.

### 1. Extension Data from URL query parameters

**Format:**

```
https://{url}/?komo_e:{unique key of extension data}={value}
```

**Examples:**

- Single string value: `https://myhub.komo.site/?komo_e:custom_unique_id=ABC123`
- JSON object: `https://myhub.komo.site/?komo_e:custom_data={"some_id":"ABC123","some_measure":123456}`

Extension data will be cleared when the session ends.

### 2. Browser EmbedSDK

Once the setup script is loaded, you will be able to use the helper methods on the `komoEmbed` javascript object to set extension data. See the instructions [here](/embedding/browser#extension-data) for more information.

### 3. React Native

See the instructions [here](/embedding/react-native#extension-data) for more information.