why most of session start events have the property 'current_url' as 'not set'
why most of session start events have the property 'current_url' as 'not set'
why most of session start events have the property 'current_url' as 'not set'
kapa.ai i have timeout based sessions. does it mean that all the not set "current_url" do not have any other events triggered?
No, it does not mean that the session had no other events. For timeout-based sessions, Mixpanel assigns properties to the Session Start event by taking the value from the first event in that session where the property is defined [Session Properties]. Therefore, if current_url is (not set), it means that none of the events triggered within that entire session contained the current_url property [Session Properties; Falsy Values]. A session could still have multiple events triggered during its duration; however, current_url will remain (not set) if:
The events came from a source that does not collect current_url: The $current_url property is automatically tracked by the JavaScript (Web) SDK, but is not automatically captured by mobile SDKs (iOS, Android, Unity) or server-side integrations [Event Properties]. If a user triggers several events on a mobile app or via backend APIs, the session will contain events, but none of them will have current_url.
Web events fired without the property: If your web events were tracked in an environment where $current_url was stripped or not populated, none of the events in the session will supply a value for Mixpanel to attribute [Falsy Values].
To verify how many events actually occurred in those sessions, you can check the built-in Session Event Count property on the Session Start event [Session Properties].
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kapa.ai so, what is the best to define landing pages with timeout based sessions?
In Mixpanel, the recommended way to define and analyze landing pages with timeout-based sessions is to build an Insights report measuring the Session Start event broken down by the Current URL property [Use Cases].
How it works
Track page views on the web: Ensure each page load captures an event (such as a Page View) using the JavaScript SDK, which automatically tracks the Current URL ($current_url) property [Use Cases; Event Properties].
Property inheritance: For timeout-based sessions, Mixpanel automatically attributes the Current URL property on the Session Start event from the first event in the session where that property is defined [Session Properties].
Breakdown by URL: In your report, select Session Start as your metric and add a Breakdown by Current URL to identify your top landing pages [Use Cases].
Best practices to ensure clean landing page data
Filter out (not set) values: If your project tracks non-web events (such as mobile app activity or server-side events) that do not collect Current URL, filter your report by setting Current URL is set or by filtering to web platforms only [Falsy Values; Event Properties].
Exclude non-user actions: In Project Settings > Overview > Session Settings, exclude background, passive, or server-triggered events (such as backend notifications) from sessions [Session Computation Deep-Dive]. If these events fire before a user lands on a web page, they can inadvertently initiate the session [Session Computation Deep-Dive].
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kapa.ai are pageviews different dedicated events that cost?
Yes, page views are dedicated events and they do count toward your billing volume.
They are dedicated events: Page view tracking is turned off by default [Track Page Views]. When enabled via the JavaScript SDK (e.g., track_pageview: true) or triggered manually with mixpanel.track_pageview(), Mixpanel sends a dedicated event typically named $mp_web_page_view (or "Page View") along with associated page properties [Track Page Views; FAQ].
They count toward billing costs: Mixpanel's default pricing is event-based and calculates your charges based on the total number of events tracked across your organization's projects [How Mixpanel Pricing Works]. Mixpanel only excludes specific system events and API updates (such as $identify, $merge, or $opt_in) from event calculations; page view events are not excluded and therefore count toward your event allowance [How Mixpanel Pricing Works].
(Note: If your organization is on an MTU-based plan, a page view is a qualifying event that counts an anonymous or identified visitor as an MTU, and it counts toward the total event volume used in the MTU guardrail calculation [MTU billing].)
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kapa.ai if i used an event_based session, would the session start event help me determine a landing page?
Yes, an Event-Based Session can help you determine a landing page, provided that the event you define as the starting event includes the page URL [Event-Based Sessions; Session Properties]. Here is how it works and what to keep in mind:
1. How properties are assigned in Event-Based Sessions
Unlike timeout-based sessions (which look through the session for the first event containing the property), an event-based session defines the session start by a specific event you choose (such as "Page View" or "Login") [Event-Based Sessions; Session Properties]. Mixpanel associates properties onto the virtual Session Start event directly from that starting event [Session Properties].
2. Requirements for tracking landing pages
For the Session Start event to determine the landing page:
Your starting event must be an event fired when a user lands on a page (such as a Page View event) [Use Cases].
That starting event must track the URL property (such as Current URL or $current_url, which is captured automatically by the JavaScript SDK) [Default Properties].
If you configure an event like "Login" as your starting event, but "Login" does not track the URL or happens after a user has already browsed pages, the Session Start event will only reflect the URL where the login action occurred rather than the true landing page.
3. Analyzing the landing page
Once your event-based session has a page-load event set as the starting event, you can build an Insights report, select the Session Start event, and break down by Current URL to see your most common landing pages [Use Cases].
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kapa.ai can I use the session start event in the formula of a custom property?
The provided knowledge sources do not explicitly state whether the virtual Session Start event can be referenced within the formula of a custom property. The documentation explains that custom properties allow you to combine existing properties (event properties and user profile properties) using formula functions, rather than referencing events themselves directly within the custom property formula [Custom Properties]. While you can create custom event properties derived from event properties, the sources do not mention if virtual events like Session Start or their associated properties can be used to construct a custom property definition. However, you can use the Session Start event directly in standard report formulas (such as dividing Page Views by Session Start in an Insights report) [Use Cases; Session Controls in Reports].
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kapa.ai if I have a borrowed property, when is its value replaced by another value?
A borrowed property’s value is replaced under the following conditions:
When a more recent source event occurs where the property is set: Borrowed Properties strictly capture the property value from the most recent event where the property is set prior to the target event [Borrowing Mechanics]. For example, if multiple source events occur before your target event, the borrowed value is replaced by the value from the most recent one [Borrowing Mechanics].
When the source event falls outside the 7-day lookback window: Mixpanel applies a fixed seven-day lookback window [Borrowing Mechanics]. If the most recent source event occurred more than 7 days before the target event, the borrowed value is replaced by (not set) [Borrowing Mechanics].
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