This document covers definitions and terminology for the Page Speed Report. Please use our Table of Contents below, or search via Ctrl / Cmd + F to find the exact term you’re looking for.
For setup instructions and details on the Page Speed Report, please see our Page Speed Check and Reading a Page Speed Report documentation.
Please note: our Page Speed Check, and its underlying metrics, analysis, and terminology are built on the Google Lighthouse framework.
Table of Contents
- Performance Metrics
- Accessibility Score
- SEO Score
- PWA Score
- Other Scoring Terms
- Total Byte Weight
- Main Thread Work
- Network Round Trip Time (RTT)
- Server Backend Latency
- DOM Size
- DOM Content Loaded
- Total Requests
- Total Requests Size
- Image Requests
- Image Requests Size
- Script Requests
- Script Requests Size
- Font Requests
- Font Requests Size
- StyleSheet Request
- StyleSheet Request Size
- Document Requests
- Document Requests Size
- Other Requests
- Other Requests Size
- Media Requests
- Media Requests Size
- Initial Server Response Time
- Final Thoughts
First Contentful Paint (FCP)
FCP measures how long it takes the browser to render the first piece of DOM content after a user navigates to your page.
Speed Index (SI)
SI measures how quickly content is visually displayed during page load.
Total Blocking Time (TBT)
TBT measures the total amount of time that a page is blocked from responding to user input.
Largest Contentful Paint (LCP)
LCP measures when the largest content element in the viewport is rendered to the screen.
Cumulative Layout Shift (CLS)
CLS measures the largest amount of layout shifts within a given amount of time. A layout shift is defined by a visible element that changes its position on a given webpage.
Time to Interactive (TTI)
TTI measures how long it takes a page to become fully interactive. This includes displaying useful content and the page responding to user interactions within 50ms.
First Meaningful Paint (FMP)
FMP measures when the primary content of a page is visible to the user.
First Input Delay (FID)
FID measures the time from when a user first interacts with a page to the time the client is able to begin processing the response to the user interaction.
Max Potential First Input Delay
Max Potential First Input Delay measures the worst-case First Input Delay that your users might experience.
Redirects happen when the browser/client requests a resource that has been moved or is otherwise in another location. While the new location of the resource is displayed in the HTTP response, this ultimately slows down your page speed. The client/browser has to then make another HTTP request to the location.
The Accessibility Scores are based on whether a page has accessibility throughout the page, in parts of the page, or not at all. Unlike the Performance Audits, Accessibility score does not provide points to a page with partial accessibility. A failing score is issued if the entire page is not accessible.
The SEO Score tally’s a page’s ability to be indexed by answering specific questions about your webpage. The following are just a few examples of the questions being answered when scoring your page:
- Does your page have a meta description?
- Does the page have descriptive link text?
- Is the page mobile friendly?
- Does the page have a valid hreflang?
PWA scores determine whether your page has the aspects of a Progressive Web App. The aspects of a progressive web app include short load times on a mobile connection, your web app works offline, and whether your web app is using HTTPS or not.
Having a progressive, responsive, and accessible web app can be a large aspect of driving traffic to your web page.
Other Scoring Terms
Total Byte Weight
The Total Byte Weight audit checks the weight of the page and its resources, without counting any request performed during the page load time.
Main Thread Work
The Main-Thread is where the browser processes most of the tasks related to your page load, like rendering/painting content or handling user interaction.
Network Round Trip Time (RTT)
RTT is the total time it takes for the HTTP request to travel over the network from the sending server and for the response to travel back from the receiving server. This time is typically measured in milliseconds.
Server Backend Latency
Backend Latency refers to the delay in transmission of data. Response time encompasses both the transmission delays and the actual processing time of the backend application.
DOM refers to the Document Object Model. The DOM is the sum of all the tags, otherwise known as nodes in your webpage’s HTML file. The larger the DOM size is, the longer your webpage will likely take to load.
DOM Content Loaded
DOM Content Loaded measures the time it takes the initial HTML document to be completely loaded and parsed, without waiting for stylesheets and images to load.
The time it takes to download and display the entire content of a web page in the browser window.
The Total Requests on a webpage are the number of HTTP requests being sent to a given server to load/render a webpage from the client.
Total Requests Size
This is the total size, in bytes, accumulated over sending the total number of requests to a given server from the client.
This is the total number of image requests sent to a given server from the client for a webpage.
Image Requests Size
The size of the total number of image requests sent to a given server from the client for a webpage, measured in bytes.
The total number of script requests sent to a given server while loading a webpage.
Script Requests Size
The size of the total number of script requests sent to a given server. This is measured in bytes.
The total number of different font requests performed on a given webpage.
Font Requests Size
The size, in bytes, of the total number of font requests performed on a given webpage.
The number of stylesheet requests made to a given server for a webpage.
StyleSheet Request Size
Defines the total size of the stylesheet requests being performed on a webpage.
Total number of document requests performed on a webpage while loading/rendering.
Document Requests Size
Defines the total size of the document requests being performed on a webpage, measured in bytes.
Other Requests include items other than the typical HTTP GET request when loading a website. Other requests can be POST, PUT, PATCH, or DELETE.
Other Requests Size
Defined by the total size of other requests being sent to a given server while loading a webpage.
Any requests for videos, social media, or otherwise are categorized as media requests.
Media Requests Size
The total size of the media requests being sent downloaded to the browser/client while loading a webpage.
Initial Server Response Time
Defined as how quickly your server responds to user requests. This can directly affect a user’s experience on your webpage. A low response time can deter users from continuing to navigate your webpage.
Understanding these terms and metrics will help you maximize the effectiveness and quality of your Page Speed Checks and subsequent reports.
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