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Synthetic Monitoring Metrics

This page lists all the website performance metrics that are available in DebugBear's synthetic monitoring feature. You can use the API ID to view metrics in the CSV export and the DebugBear API.

This list also includes the real-user Google CrUX metrics that are collected as part of every lab test.

Synthetic monitoring charts

Available synthetic metrics

DebugBear RUM currently supports 129 different synthetic metrics.

tip

You can access specific CrUX metrics with keys like crux.origin.fcp.p75 or crux.cls.bad. However, we have not listed these metrics here individually.

HTTP Request TTFB

Server response time measures how long after sending the HTTP request for the HTML document the first byte of the response was received. It does not include time spent establishing the server connection. TTFB is short for Time to First Byte. More details.

API ID: requestTtfb

Full TTFB

The Full Time to First Byte measures how quickly the server responds to the HTML document request. This includes time spent establishing a server connection or on redirects. More details.

API ID: performance.ttfb

Document Duration

Duration of the entire document request, including establishing a connection and download time. In contrast, the TTFB metric does not include time spent downloading the full response.

API ID: documentDuration

Largest Contentful Paint

Largest Contentful Paint measures how quickly the largest page element appears. This could be a hero image or a big heading. More details.

API ID: performance.largestContentfulPaint

First Contentful Paint

First Contentful Paint measures how quickly content appears on the page after navigation. For example, text and images count as content. More details.

API ID: performance.firstContentfulPaint

First Paint

The First Paint measures when the page first rendered. Unlike First Contentful Paint, First Paint also counts non-contentful paints, for example a box with a gray background.

API ID: firstPaint

Speed Index

Speed Index measures how quickly most of the page content is rendered. Unlike Largest Contentful Paint it does not focus on a single UI element being rendered but instead looks at the whole screen. More details.

API ID: performance.speedIndex

Time to Interactive

Time to Interactive measures when the network and CPU usage of the page becomes idle. Generally, all functionality on the page is then ready to use. More details.

API ID: performance.interactive

Load Event

The load event marks the time when the page has loaded including any dependent resources like scripts and images. While the Load event has long been used as a page speed metric, it was not designed to be one. Where possible, prefer a paint timing metric like FCP or LCP. More details.

API ID: load

DOMContentLoaded

The DOMContentLoaded event timing measure when the initial page HTML has been parsed. This milestone occurs before dependent resources like async scripts or images are loaded. More details.

API ID: domContentLoaded

Total Blocking Time

Total Blocking Time measures how responsive your site is to user input. It considers the page as blocked if a CPU task takes over 50 milliseconds. More details.

API ID: performance.totalBlockingTime

Cumulative Layout Shift

Cumulative Layout Shift measures how stable the page layout is. Layout instability is when content shifts around on the page after being rendered. More details.

API ID: performance.cumulativeLayoutShift

DOM Nodes

The number of DOM page elements on the page.

API ID: nodes

OuterHTML Size

Length of the document outerHTML property.

API ID: outerHtmlLength

JS Event Listener Count

Number of registered event listeners on the page

API ID: jsEventListeners

Recalc Style Count

Total number of full or partial style recalculations.

API ID: recalcStyleCount

Layout Count

Total number of full or partial page layouts.

API ID: layoutCount

Performance

The Performance score from Google's Lighthouse tool aggregates 6 different performance metrics. More details.

API ID: performance.score

Accessibility

Lighthouse checks pages for various accessibility issues and assigns a grade between 0 and 100. More details.

API ID: accessibility.score

Best Practices

Lighthouse checks that the page follows various best practices like using HTTPS and not requesting unnecessary permissions.

API ID: bestPractices.score

SEO

This score grades how well the page follows basic search engine optimization advice. More details.

API ID: seo.score

Request Count

The total number of network requests made when loading the page.

API ID: requestCount

Third Party Bytes

Amount of data loaded from known third parties, for example analytics providers or shared CDNs.

API ID: thirdParty.bytes

Third Party CPU

Amount main thread CPU time that's attributable to third-party resources.

API ID: thirdParty.ms

Third Party Count

Number of unique third parties identified.

API ID: thirdParty.count

CPU Time

Total amount of time the browser main thread was busy while loading the page. More details.

API ID: cpu.total

JS Time

Time spent parsing, compiling, and running JavaScript code. More details.

API ID: jsTime

CPU (Other)

Other unattributed CPU processing time.

API ID: cpu.other

CPU (Parse/Compile JS)

Time spent parsing and compiling JavaScript.

API ID: cpu.scriptParseCompile

CPU (Run JS)

Time spent running JavaScript code.

API ID: cpu.scriptEvaluation

CPU (Parse HTML)

Time spent parsing HTML code.

API ID: cpu.parseHTML

CPU (Style/Layout)

CPU time spent on style and layout calculations necessary to render page content.

API ID: cpu.styleLayout

CPU (Garbage Collection)

Time spent on garbage collection. Garbage collection happens in the background to free up memory on the page.

API ID: cpu.garbageCollection

CPU (Paint)

Time spent on painting the page. Painting is the process of filling in pixels on the screen.

API ID: cpu.paintCompositeRender

Page Weight (Total)

Page weight measures the size of the resources being downloaded when loading the page, for example images or JavaScript files. More details.

API ID: pageWeight.total

Page Weight (HTML)

The total size of the main document HTML file and iframe HTML loaded on the page. More details.

API ID: pageWeight.document

Page Weight (CSS)

The total size of CSS files loaded on the page. More details.

API ID: pageWeight.stylesheet

Page Weight (JavaScript)

The total size of JavaScript files loaded on the page. More details.

API ID: pageWeight.script

Page Weight (Images)

The total size of images loaded on the page. More details.

API ID: pageWeight.image

Page Weight (Fonts)

The total size of font files loaded on the page. More details.

API ID: pageWeight.font

Page Weight (Ajax)

The total download size of XHR and fetch responses on the page. More details.

API ID: pageWeight.ajax

Page Weight (Redirects)

The total data transfer due to redirects. More details.

API ID: pageWeight.redirect

Page Weight (Media)

The total size of video and audio files loaded on the page. More details.

API ID: pageWeight.media

Page Weight (Other)

The total size of other resources loaded on the page. More details.

API ID: pageWeight.other

Resource Hint Errors

Resource Hints can speed up your website by telling the browser about resources before they are naturally discovered. But poorly used resource hints can also slow your website down. More details.

API ID: hints.errors

Resource Hints

Number of resource hints on the page. For example, preconnect, preload, or prefetch. More details.

API ID: hints.count

Console Messages

The total number of console messages recorded on the page.

API ID: console.messages

Console Logged Errors

The number of error messages in the browser console.

API ID: console.errors

Console Errors

The number of error messages and exceptions in the browser console.

API ID: console.totalErrors

Page Errors

The number of JavaScript exceptions thrown on the page.

API ID: console.pageerrors

Console Warnings

The number of warning messages in the browser console.

API ID: console.warnings

Console Other

The total number of console messages recorded on the page that are not logs, warnings, or errors. This category includes debug messages, timings, info, and group messages.

API ID: console.other

Console Logs

The total number of standard log entries recorded on the page (in contrast to errors or warnings).

API ID: console.logs

Visually Complete

The Visually Complete milestone marks when the page has been fully rendered and no additional visual changes occur. More details.

API ID: visuallyComplete

Cumulative Layout Shift (CrUX)

The Cumulative Layout Shift metric measures how stable the page layout is and whether content shifts around after being rendered. More details.

API ID: crux.cls.p75

First Contentful Paint (CrUX)

The First Contentful Paint metric measures how soon after navigating to the page the first content element appeared, for example text or an image. More details.

API ID: crux.fcp.p75

Largest Contentful Paint (CrUX)

The Largest Contentful Paint metric measures how soon after navigating to the page the largest content element appeared. More details.

API ID: crux.lcp.p75

Interaction to Next Paint (CrUX)

Interaction to Next Paint measures how quickly the page updates after the user interacts with it. More details.

API ID: crux.inp.p75

Time to First Byte (CrUX)

Time to First Byte measures how soon the browser received a response for the HTML document request. More details.

API ID: crux.ttfb.p75

Image TTFB (CrUX) — URL

Time to First Byte measures how soon the browser received a response for the HTML document request. More details.

API ID: crux.url.imageTtfb.p75

Load Delay (CrUX) — URL

If the LCP element is an image the load delay measures how long after the document TTFB the image resource is discovered by the browser. More details.

API ID: crux.url.lcpLoadDelay.p75

Load Duration (CrUX) — URL

If the LCP element is an image the resource load time measures how long it takes to request and download the image. More details.

API ID: crux.url.lcpLoadDuration.p75

Render Delay (CrUX) — URL

The render delay measures how long it takes for the LCP element to become visible. More details.

API ID: crux.url.lcpRenderDelay.p75

Round Trip Time (CrUX)

The estimated network round trip time indicates how long it takes for data to travel between the user's device and the server. More details.

API ID: crux.rtt.p75