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Performance: Terminology

Modified on: Tue, 13 Feb, 2024 at 11:45 PM

The Siteimprove Performance feature allows you to audit and optimize your website for improved load time performance.  Improving the load times of your content will allow you to deliver a better experience for your visitors, improving retention and conversion rates and making your content more effective. This article explains some of the terms used in the Performance feature.

First Contentful Paint (FCP)The time it takes for the web browser to load, render and display the first bit of content on the page. This provides the user with the first indication that something is happening on the page.  FCP also marks when the browser goes from whitespace to partial content being visible on the page.

The time stamp is based on how long it takes the browser to render any text, image (including background images), non-white canvas or SVG. This excludes iframes but includes web fonts that are pending.

Largest Contentful Paint (LCP)

The time it takes for the web browser to load, render and display the largest image or block of context within the user's viewport. Anything that extends beyond the viewport is not included in this metric. This provides an overview of how long users will have to wait for the primary content of the page.

The time stamp is based on how long it takes for the browser to load, render and display the main content of a page, i.e. elements that make up the majority of the primary content on the page within the user's viewport.  Typical elements include images, videos, background images, and block-level text. 

Visitor Profile

A combination of parameters used to generate a measurement.  These include the type of device being simulated, the network with which the test is run, and the location from which the measurement will be carried out.  Each visitor profile, therefore, represents a unique combination of factors, and this allows you to represent a myriad of different visitor situations in order to determine where your performance should be improved.


A method of encoding content in such a way that the file sizes are reduced, which results in a smaller amount of data that needs to be served to users.  This, in turn, leads to a faster load and less time spent waiting for content to appear on the page.

Examples of file types that can be compressed include text, images, and fonts.  There are many different techniques to choose from in order to enable compression, and some modern CMS systems support plug-ins that greatly speed up the process.


A method of storing common files and resources closer to the user, so that these don’t have to be re-downloaded upon consecutive site visits. By preventing this, we ensure as fast of an experience as possible for our users.

For our purposes, we can divide the area into two sub-categories; browser caching and server-side caching.  Browser caching means that the web browser will store certain items like CSS files, images, and logos, in order to speed up future visits of your site.

Server-side caching means that it’s the server storing common items instead of the browser, which are then served to several users faster than traditional access.


A methodology whereby we defer the loading of items and files until they are needed by the user.  This will speed up the initial load since we are not having to load in objects and files which the user might not need.

Common examples include deferring the loading of images that are not visible initially to the user (such as image grids outside of the user's viewport at the bottom of the page). These images would then instead be loaded as the user scrolls down the page.


A method for reducing the size of resources used by the website, in order to

Examples include reformatting CSS and Javascript files to remove comments, unused code, and use shorter variable and function names.  There are many free tools available that can minify HTML, CSS and Javascript for your site.

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