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Tracking events

Designing how and what to track in your app is an important decision. Check out our docs about tracking design here.

Snowplow has been built to enable you to track a wide range of events that occur when users interact with your apps.

We provide several built-in events to help you track different kinds of events. When instantiated, their objects can be passed to the tracker.track() method to send events to the Snowplow collector. The events range from single purpose ones, such as ScreenViewEvent, to the more complex but flexible SelfDescribingEvent, which can be used to track any kind of user behavior. We strongly recommend using SelfDescribingEvent for your tracking, as it allows you to design custom event types to match your business requirements. This post on our blog, "Re-thinking the structure of event data" might be informative here.

Event classes supported by the Rust Tracker:

MethodEvent type tracked
SelfDescribingEventCustom event based on "self-describing" JSON schema
StructuredEventSemi-custom structured event
ScreenViewEventView of a screen in the app
TimingEventUser timing events such as how long resources take to load.

All the methods share common features and parameters. Every type of event can have an optional context added. See the next page to learn about adding extra data to events. It's important to understand how event context works, as it is one of the most powerful Snowplow features. Adding event context is a way to add depth, richness and value to all of your events.

Snowplow events are all processed into the same format, regardless of the event type (and regardless of the tracker language used). Read about the different properties and fields of events in the Snowplow Tracker Protocol.

We will first discuss the custom event types, followed by the out-of-the-box event types. Note that you can also design and create your own page view, or screen view, using SelfDescribingEvent, to fit your business needs better. The out-of-the-box event types are provided so you can get started with generating event data quickly.

Track self-describing events with SelfDescribingEvent

Use the SelfDescribingEvent type to track a custom event. This is the most advanced and powerful tracking method, which requires a certain amount of planning and infrastructure.

Self-describing events are based around "self-describing" (self-referential) JSONs, which are a specific kind of JSON schema. A unique schema can be designed for each type of event that you want to track. This allows you to track the specific things that are important to you, in a way that is defined by you.

This is particularly useful when:

  • You want to track event types which are proprietary/specific to your business
  • You want to track events which have unpredictable or frequently changing properties

A self-describing JSON has two keys, schema and data. The schema value should point to a valid self-describing JSON schema. They are called self-describing because the schema will specify the fields allowed in the data value. Read more about how schemas are used with Snowplow here.

After events have been collected by the event collector, they are validated to ensure that the properties match the self-describing JSONs. Mistakes (e.g. extra fields, or incorrect types) will result in events being processed as Bad Events. This means that only high-quality, valid events arrive in your data storage or real-time stream.


Your schemas must be accessible to your pipeline to allow this validation. See Managing data structures for information on how to create and update schemas.

Example (assumes that tracker is a tracker instance created using Snowplow::create_tracker):

// Tracking a Self-Describing event with context entity
let self_describing_event = SelfDescribingEvent::builder()
.data(json!({"name": "test", "id": "something else"}))

let event_context = Some(vec![SelfDescribingJson::new(
json!({"keywords": ["tester"]}),

let self_desc_event_id = tracker.track(self_describing_event, event_context)?;

Track structured events with StructuredEvent

This method provides a halfway-house between tracking fully user-defined self-describing events and out-of-the box predefined events. This event type can be used to track many types of user activity, as it is somewhat customizable. "Struct" events closely mirror the structure of Google Analytics events, with "category", "action", "label", and "value" properties.

As these fields are fairly arbitrary, we recommend following the advice in this table how to define structured events. It's important to be consistent throughout the business about how each field is used.

ArgumentDescriptionRequired in event?
categoryThe grouping of structured events which this action belongs toYes
actionDefines the type of user interaction which this event involvesYes
labelOften used to refer to the 'object' the action is performed onNo
propertyDescribing the 'object', or the action performed on itNo
valueProvides numerical data about the eventNo


// Tracking a Structured event
let structured_event = StructuredEvent::builder()
.label("Add To Basket")

let struct_event_id = tracker.track(structured_event, None)?;

Track screen views with ScreenViewEvent

Use ScreenViewEvent to track a user viewing a screen (or similar) within your app. This is the page view equivalent for apps that are not webpages. The arguments are nameidtype, and transitionType. The name and id properties are required. "Name" is the human-readable screen name, and "ID" should be the unique screen ID (UUID v4).

This method creates an unstruct event, by creating and tracking a self-describing event. The schema ID for this is "iglu:com.snowplowanalytics.snowplow/screen_view/jsonschema/1-0-0", and the data field will contain the parameters which you provide. That schema is hosted on the schema repository Iglu Central, and so will always be available to your pipeline.

ArgumentDescriptionRequired in event?
nameThe name of the screen viewed.Yes
idThe id (UUID v4) of screen that was viewed.Yes
typeThe type of screen that was viewed.No
previousNameThe name of the previous screen that was viewed.No
previousTypeThe type of screen that was viewed.No
previousIdThe id (UUID v4) of the previous screen that was viewed.No
transitionTypeThe type of transition that led to the screen being viewed.No


// Tracking a Screen View event
let screen_view_event = ScreenViewEvent::builder()
.name("a screen view")
.previous_name("previous name")

let screen_view_event_id = tracker.track(screen_view_event, None)?;

Track timing events with TimingEvent

Use the TimingEvent type to track user timing events such as how long resources take to load. These events take a timing category, the variable being measured, and the TimingEvent time measurement. An optional label can be added to further identify the timing event

ArgumentDescriptionRequired in event?
categoryDefines the timing category.Yes
variableDefines the timing variable measured.Yes
timingRepresents the time.Yes
labelAn optional string to further identify the timing event.No


let timing_event = TimingEvent::builder()
.label("Time to fetch map resource")

let timing_event_id = tracker.track(timing_event, None)?;
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