Capture event and session properties for web frontends

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How-to guide
Published Nov 11, 2025
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Event and session properties let you attach custom-defined key-value pairs to user events and user sessions, using the namespaces event_properties and session_properties.

Before you start sending event or session properties

Event and session properties must be configured before they can be used. Incoming event and session properties that are not configured are dropped during event ingest.

To configure an event or session property

In Experience Vitals, select the frontend for which you want to add the property.
In the Settings tab, select Event and session properties.
Depending on whether you want to configure an event or session property, select Add under either Defined event properties or Defined session properties.
In Field name, specify a name, for example cart.total_value.
If you want field name validation to be case insensitive, turn on Field name validation should be case-insensitive.
Under Datatype, select one of the available types—either string, boolean, or number.

Note that the field name is always prefixed with either event_properties. or session_properties., depending on the selected type, for example event_properties.cart.total_value

How to send properties

Event and session properties can be sent via the JavaScript API:

To add event properties, use addEventModifier.
To send a session property, use sendSessionPropertyEvent.

Limits

Naming
- Field name maximum length: 100 characters (including the event_properties. / session_properties. prefix).
- Allowed characters in field name: A–Z, a–z, 0–9, underscore _, and dot ..
Counts
- Maximum of 20 event and session properties can be configured.
Values
- For event and session properties of data type string, the length is limited to 1000 characters.