Browser Real User Monitoring Metrics

This document covers metrics used in Browser Real User Monitoring. These metrics include Core Web Vitals (CWV), Timing, Asynchronous JavaScript and XML (AJAX), and Resource timing metrics.

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Core Web Vital Metrics

Google Core Web Vitals (CWV) is a set of metrics that measure the real-world user experience for loading performance, interactivity, and visual stability of the page. Google refers to Core Web Vitals as one of the signals to rank webpages, which maintains healthy metrics for your website. For more information, see Core Web Vitals.

Core Web Vitals metrics include:

Name	Available For ...	Definition
Loading: First Contentful Paint (FCP)	App Base Pages	This metric measures when a page starts to load to when any part of the page content is rendered on the screen.
Interactivity: First Input Delay (FID)		This metric measures the time from when a user first interacts with a page (when you click a link, tap on a button, or use a custom JavaScript-powered control) to the time when the browser begins process event handlers in response to the interaction.
Loading: Largest Contentful Paint (LCP)		This metric reports the render time of the largest image or text block visible within the viewport relative to when the page first started loading.
Visual Stability: Cumulative Layout Shift (CLS)		This is a measure of the largest burst of layout shift scores for every unexpected layout shift that occurs during the lifespan of a page.

Timing Metrics

Timing metrics include:

Name	NavTiming Capable Browsers¹	Available For ...	Definition
AJAX Callback Execution Time (DPT)	`responseEnd` to `endTimeUnixNano`	AJAX Requests (XHR, Fetch API)	Time for the browser to process the AJAX response. This includes the time to apply the response data to the Document Object Model (DOM).
AJAX Response Download Time (DDT)	`responseStart` to `responseEnd`	AJAX Requests (XHR, Fetch API)	Time for the browser to download the complete AJAX response.
AJAX Request Errors per Minute	N/A	AJAX Requests (XHR, Fetch API)	Total number of AJAX requests that generate an error per minute.
DOM Building Time (DPT)	`responseEnd` to `domContentLoadedEventStart`	Base Pages Iframes	Time for the browser to build the DOM and make it available for JavaScript to apply rendering logic.
DOM Ready Time (DOM)	`fetchStart` to `domContentLoadedEventStart`	Base Pages Iframes	Interval between the time that a user initiates a request and the time that the `DOMContentLoaded` event (or the internal handler's `onready` event) occurs.
Domain Lookup Time (DNS)	`domainLookupStart` to `domainLookupEnd`	Base Pages Iframes	Time to complete the domain lookup of the server connection time.
End User Response Time	`fetchStart` to `loadEventEnd`	AJAX Requests (XHR, Fetch API) App Base Pages Iframes	Average interval between the time that a user initiates a request and the completion of the page load of the response in the user's browser. In the context of an AJAX request, it ends when the response has been completely processed. For information about End User Response Time for SPA2 pages, see SPA2 Metrics.
First Byte Time (FBT)	`fetchStart` to `responseStart`	AJAX Requests (XHR, Fetch API) Base Pages Iframes	Interval between the time that a user initiates a request and the time that the browser receives the first response byte. In the context of an AJAX request, First Byte Time is the interval between the AJAX request dispatch and the time that the browser receives the first response byte.
Front End Time (FET)	`responseStart` to `loadEventEnd`	Base Pages Iframes	Interval between the arrival of the first byte of text response and the completion of the response page rendering by the browser. Includes HTML Download, DOM Building Time, and Resource Fetch Time.
HTML Download Time (DDT)	`responseStart` to `responseEnd`	Base Pages Iframe	Time for the browser to download the complete HTML document content.
Resource Fetch Time	`domContentLoadedEventStart`to `loadEventEnd`	Base Pages Iframes	Time for the browser to complete the download of remaining resources, including images, and finish rendering the page.
Requests per Minute (Short name based on PLC entries)	N/A	AJAX Requests (XHR, Fetch API) App Base Pages Iframes	Total number of requests (Page + AJAX + Iframe) per minute.
Server Connection Time (SCT)	`fetchStart` to `requestStart`	Base Pages Iframes	Interval between the time a user initiates a request and the start of fetching the response document from the server or application task. Includes the time spent on redirects, domain lookups, TCP connects, and SSL handshakes.
SSL Handshake Time (SSL)	`secureConnectionStart` to `connectEnd`	Base Pages Iframes	Time taken to complete the SSL handshake.
TCP Connect Time (TCP)	`connectStart` to `connectEnd`	Base Pages Iframes	Time to complete the TCP connect portion of the server connection time, the equivalent of one network roundtrip of latency.
Visually Complete Time (VCT)	N/A	App Base Pages Iframes	Total time for all visual elements within the first screen (above-the-fold content) to load in an end user’s browser. Calculated using the last visual change to the page in a browser window. For information about Visually Complete Time for SPA2 pages, see SPA2 Metrics.

AJAX Metrics

These four core metrics are always available regardless of the browser type because the AJAX requests occur when there are a large number of pages.

AJAX metrics include:

End User Response Time
First Byte Time
AJAX Response Download Time
AJAX Callback Execution Time

Ajax Core Metrics Diagram

For more information on which browsers support the Navigation Timing API, see the Can I Use website.

Resource Timing Metrics

Resource timing metrics are the median times in milliseconds. Resource metrics include:

Name	Calculation	Description
Browser Wait Time	`fetchStart` to `domainLookupStart`	Time from the redirection or request start until the browser begins to fetch the resource.
Content Download Time	`responseStart` to `responseEnd`	Interval between the time that a user initiates a request and the time that the event occurs.
DNS Lookup	`domainLookupStart` to `domainLookupEnd`	Time from when the browser starts to fetch the resource until the browser starts the domain name lookup for the resource.
Initial TCP Connection	`connectStart` to `secureConnectionStart`	Time to complete the establish the TCP connection for a resource: the equivalent of one network roundtrip of latency.
Request Pending	`connectEnd` to `requestStart`	Time for the browser to complete the request for a resource from the server, cache, or local resource.
Request and Wait	`requestStart` to `responseStart`	Time for the request is made for a resource from the server, cache, or local resource before the connection is closed.
SSL/TLS Handshake	`secureConnectionStart` to `connectEnd`	Time to establish a secure connection to the server.