> For the complete documentation index, see [llms.txt](https://docs.tebex.io/developers/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tebex.io/developers/headless-api/guides/baskets/add-package-to-basket/custom-data.md).

# Custom Data

Tebex supports `custom` data when adding packages to the basket. All `custom` data will be returned to you in associated Webhooks that deliver basket information.

```json
{
    "package_id": "6276316",
    "quantity": 1,
    "variable_data": {
        "username_id": "9e65a968ee4743d19a2a4c9969154491"
    },
    "custom": {
        "key": "value"
    }
}
```

Custom data is useful to assist with integration into your own systems. 

Common use cases for custom data include custom user identifiers. Your website could authorize a user in-house, then attach their user ID which will be provided to all webhook receivers. This would enable your backend server to quickly reference your internal models.