> ## Documentation Index
> Fetch the complete documentation index at: https://launchdarkly.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Reserved custom properties

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This topic explains how to use the reserved custom properties integration framework capability.

## About reserved custom properties

Custom properties let you store data in LaunchDarkly alongside a feature flag. For example, you can use custom properties to indicate flag-level associations with data on your service. If you don't have any flag-level associations or configurations, you don't need to use this capability.

To learn more, read [Custom properties](/docs/home/infrastructure/custom-properties).

By default, members must specify a custom property name and key when they attach the custom property value to a feature flag. This step introduces the possibility of user error. To prevent this, developers can "reserve" a custom property for their integration, which makes it much easier for members to correctly add the property's value to feature flags.

`reservedCustomProperties` require a `name` and `key`. Adding a `description` is optional.

After a member configures your integration, the custom property appears in the dropdown in the flag's right sidebar.

For example, the [Datadog integration](https://github.com/launchdarkly/integration-framework/blob/main/integrations/datadog/manifest.json) uses the following `reservedCustomProperties`:

<CodeGroup>
  ```json title="The reservedCustomProperties capability" lines wrap theme={null}
      "reservedCustomProperties": [
        {
          "name": "Datadog tags",
          "description": "Tags are a way of adding additional dimension...",
          "key": "datadog"
        }
      ]
  ```
</CodeGroup>