User action metrics
For web applications, Dynatrace calculates a host of user action metrics.
The following metrics are core web vitals and are available only for load actions:
- Largest contentful paint
- Cumulative layout shift
- First input delay
Milestone metrics represent events that occur at a specific point in time during a user action. However, these metrics are measured in seconds or milliseconds because they are calculated relative to the user action start time. In other words, user action start time serves as a reference point from which the time for the milestone metrics is measured. For example, a value of 47 ms for Navigation start indicates that this event occurred 47 ms after the action start time.
The moment when the user agent finishes prompting to unload the previous page
The time before the user agent sends the request to obtain the page from the server, relevant application caches, or a local resource
Time to first byte
The time taken until the first byte of the response is received from the server, relevant application caches, or a local resource
The time taken until the user agent receives the last byte of the response or the transport connection is closed, whichever comes first
The time taken until the page's status is set to "interactive" and it's ready to receive input
The score measuring how quickly the visible parts of the page are rendered
DOM content loaded
The time taken until the user agent fires the
The time taken to render the first non-default background element
First contentful paint3
The time taken to render the first bit of content, such as text or images
Largest contentful paint4
The time taken to render the largest element in the viewport
The time taken to fully render content in the viewport
The time taken until the page's status is set to "complete"
Load event start
The time taken to begin the load event of the page
Load event end
The time taken to complete the load event of the page
User action duration
The time taken to complete the page load
First input start
The moment when the user first interacts with a page, for example, clicks a UI control
First input delay5
The time from the first interaction with the page to when the user agent can respond to that interaction
Speed index and Visually complete are only available on browsers that support mutation observers: Microsoft Internet Explorer 11, Microsoft Edge 15+, Firefox 57+, and Google Chrome 61+.
First paint is supported on all browsers except Internet Explorer.
First contentful paint is available only for Chromium-based browsers.
Largest contentful paint is available for Chromium-based browsers. Measured using Google-provided APIs.
For Chromium-based browsers, First input delay is measured using Google-provided APIs. For Firefox, Safari, and Internet Explorer 9+, the metric is measured using a Dynatrace implementation that listens for events of type
As opposed to milestone metrics, phase metrics imply a duration.
The time between when the user agent receives a request to download a resource and when it actually starts downloading the resource
The time spent checking any relevant application caches
The time taken to resolve the hostname for a target URL
The time taken to establish a TCP connection to the server (including SSL)
The time taken to secure the connection established to the server
The time taken to request the page from the server until the first byte is received
The time taken to receive the response
The time between DOM loading and Load event start
The time taken to process the load event
The time taken to execute
The time taken to execute XHR callbacks
The time taken to follow any HTTP redirects
You can use the Long tasks metric instead of the Total blocking time metric, which we decided not to introduce due to certain technical limitations. Also note that the Blocking metric shown in the waterfall isn't related to Total blocking time and is only available for specific requests.
Key performance metrics
From the metrics listed above, Dynatrace has specified some as key metrics. Key performance metrics enable you to select the ideal user experience metric for each of your applications. These key metrics provide you with valuable performance insights that promote success in your digital business. The key performance metrics include:
- User action duration
- Visually complete
- Speed index
- DOM interactive
- Load event end
- Load event start
- HTML downloaded / Response end
- Time to first byte
- Largest contentful paint
- Cumulative layout shift1
- First input delay (RUM web only)
Dynatrace allows you to choose the right performance metric for each application condition.
Missing metric measurements
Metric measurements might be missing in the following cases:
- During a load action, the user selects another link that triggers a new load action before the original page load event is completed. The second load action interrupts the Visually complete calculation of the first load action, so no measurement is available.
In the earlier version of Visually complete, Dynatrace used the user action duration as a fallback measurement. This skewed the timeseries, so such cases are now excluded to ensure more accurate aggregates.
- A late redirect is triggered immediately following a load action.
- The Visually complete time-out is reached during the calculation.
Core web vitals
- The browser API doesn't trigger and provide a metric measurement before the user action ends (see the User action duration metric).
- The user's browser doesn't support the APIs that are used to measure core web vitals. See details under Milestone metrics to learn which browsers support Core web vitals.
- The page is loaded or reloaded in an inactive tab, and the browser API does not report values.
- The browser API provides negative values.