User action metrics

For web applications, Dynatrace calculates a host of user action metrics.

Core web vitals

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

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.

Metric	Description	Applicable to
Navigation start	The moment when the user agent finishes prompting to unload the previous page If there is no previous page, this value is the same as `PerformanceTiming.fetchStart`.	Load actions
Request start	The time before the user agent sends the request to obtain the page from the server, relevant application caches, or a local resource If the transport layer fails and the connection is reopened, this metric is set to the time corresponding to the new request.	Load actions XHR actions
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	Load actions XHR actions
HTML downloaded	The time taken until the user agent receives the last byte of the response or the transport connection is closed, whichever comes first For XHR actions, this metric is known as Response end.	Load actions XHR actions
DOM interactive	The time taken until the page's status is set to "interactive" and it's ready to receive input	Load actions
Speed index¹	The score measuring how quickly the visible parts of the page are rendered	Load actions
DOM content loaded	The time taken until the user agent fires the `DOMContentLoaded` event at the page The `DOMContentLoaded` event is executed when the basic HTML of the page is loaded and its parsing is complete. The event doesn't wait for the loading of add-ons (for example, stylesheets, sub-frames, and images) to be complete.	Load actions
First paint²	The time taken to render the first non-default background element	Load actions
First contentful paint³	The time taken to render the first bit of content, such as text or images	Load actions
Largest contentful paint⁴	The time taken to render the largest element in the viewport	Load actions
Visually complete¹	The time taken to fully render content in the viewport	Load actions XHR actions
DOM complete	The time taken until the page's status is set to "complete"	Load actions
Load event start	The time taken to begin the load event of the page	Load actions
Load event end	The time taken to complete the load event of the page	Load actions
User action duration	The time taken to complete the page load This includes load time of XHR requests initiated before `loadEventEnd` and load time of dynamic resources and script executions triggered by DOM modifications.	Load actions XHR actions Custom actions
First input start	The moment when the user first interacts with a page, for example, clicks a UI control	Load actions
First input delay⁵	The time from the first interaction with the page to when the user agent can respond to that interaction	Load actions

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.

⁴

Largest contentful paint is available for Chromium-based browsers. Measured using Google-provided APIs.

⁵

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 click, mousedown, keydown, or touchstart and calculates the delay from when the RUM JavaScript registers such events to when the events are triggered.

Phase metrics

As opposed to milestone metrics, phase metrics imply a duration.

Metric	Description	Applicable to
Blocking	The time between when the user agent receives a request to download a resource and when it actually starts downloading the resource This includes the time spent on waiting for a free TCP socket, generating disk cache entries, and proxy negotiation.	Load actions
Application cache	The time spent checking any relevant application caches This includes the time before the connection to the server is established.	Load actions
DNS lookup	The time taken to resolve the hostname for a target URL	Load actions
TCP connect	The time taken to establish a TCP connection to the server (including SSL)	Load actions
Secure connect	The time taken to secure the connection established to the server This includes the SSL handshake and SOCKS.	Load actions
Request	The time taken to request the page from the server until the first byte is received	Load actions
Response	The time taken to receive the response	Load actions
Processing	The time between DOM loading and Load event start	Load actions
OnLoad	The time taken to process the load event	Load actions
OnDOMContentLoaded	The time taken to execute `onDomContentLoaded` handlers	Load actions
Callback	The time taken to execute XHR callbacks	Load actions
Redirect time	The time taken to follow any HTTP redirects	Load actions
Long tasks¹	The total time of all long JavaScript tasks (over 50 ms) The metric is measured from Navigation start for the entire user action duration.	Load actions

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)

Cumulative layout shift is the score measuring the unexpected shifting of visible webpage elements. It is available for Chromium-based browsers and measured using Google-provided APIs.

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:

Visually complete

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).
In earlier versions of Dynatrace Real User Monitoring, these values were sent after the completion of the user action. Such values were not meaningful and often not representative. For example, First input delay (FID) measures page load responsiveness. The primary driver for a high FID value is JavaScript execution. So if a user waited a minute following a page load before selecting a new link, most if not all JavaScript processing would already have taken place and the resulting small FID measurement wouldn't be a representative value of a true page load. Such measurements skewed the overall metric aggregate.
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.