Web performance terms

A/B testing is a method of comparing two versions of a webpage to see which one performs better. For example, an e-commerce store might show 50% of its visitors a green "Buy Now" button (Version A)…

Abandonment Rate is a metric that measures the percentage of users who start a specific process (like a checkout funnel or a sign-up form) but leave before completing it.

This is a term originally from newspaper design that now refers to the portion of a webpage that is visible to a user without having to scroll down. Content "above the fold" is the very first thing a user sees.

The acceleration rate is a key performance indicator specific to Speed Kit that measures the percentage of whitelisted page views that were successfully accelerated by the Service Worker.

Anonymous HTML is a generic, non-personalized version of a webpage that Speed Kit's backend creates and caches. To make a dynamic page cacheable, Speed Kit first fetches it in a way that simulates…

An anti-flicker script is a piece of JavaScript used by many Client-Side A/B Testing tools. Its purpose is to prevent the Flicker Effect, where a user briefly sees the original page before the test…

Async (asynchronous) requests are requests for CSS or JavaScript files that are loaded in the background without blocking the browser from rendering the rest of the page.

AVIF (AV1 Image File Format) is a modern, next-generation image format that provides significantly better compression than older formats like JPEG and WebP.

The back/forward cache (or bfcache) is a browser optimization that enables instant navigations when a user clicks the back or forward buttons.

The backend refers to the server-side components of a web application that are not visible to the end-user. This includes the web server, application logic, and databases.

This is Speed Kit's central, primary cache where Anonymous HTML and other website assets are stored. It is hosted on Amazon Web Services (AWS), a secure and highly reliable cloud computing platform.

Backend Time is the duration it takes for a website's Origin Server to process a request and generate the HTML for a page.

Baseline is a standard that indicates when a web platform feature is broadly supported and safe to use across all major browsers.

A beacon is a small, asynchronous packet of data that a website sends to a server for tracking or analytics purposes. In the context of Real User Monitoring (RUM), a RUM beacon is sent from the use…

Below the fold refers to all the content on a webpage that is only visible to the user after they scroll down. Because this content is not critical for the initial view, its loading should be defer…

Blocking (or render-blocking) requests are requests for CSS or JavaScript files that the browser must download, parse, and execute before it can continue rendering the rest of the page.

A Bloom filter is a highly efficient, probabilistic data structure that Speed Kit uses to keep the Service Worker Cache in the browser synchronized with the server.

Bounce Rate is the percentage of single-page sessions, meaning sessions where a user leaves your site after viewing only one page without taking any further action.

This is a measurement artifact that can occur when A/B testing website speed. "Bounce rate" refers to the percentage of visitors who leave a site after viewing only one page.

Breakpoints are the specific screen widths used in Responsive Design that trigger a change in a website's layout. They are defined in CSS media queries to adapt the design for different device cate…

Brotli is a modern compression algorithm developed by Google that generally offers better compression ratios than gzip for text-based assets like HTML, CSS, and JavaScript.

Browser Time refers to the work the user's own device (desktop or mobile) must do to turn website code into a visible and interactive page.

A cache is a high-speed, temporary storage layer designed to store copies of website files (like HTML, images, and scripts) closer to the user.

Cache contamination is a critical issue where a caching system incorrectly stores and serves personalized or user-specific content to the wrong users.

The cache hit ratio is the percentage of requests that a cache can successfully serve from its stored content (a "hit"), as opposed to requests that it cannot fulfill and must pass on to the Origin Server (a "miss").

Cache hotness is a metric that indicates how frequently a specific item in the cache is accessed. Speed Kit can use this information to optimize its processes.

Cache revalidation is the process a cache uses to check with the Origin Server to verify if a stored file is still up-to-date.

Cache-Control is an essential HTTP header that dictates the caching policy for a resource. It contains directives (e.g., max-age, no-cache, no-store) that instruct browsers and intermediate caches…

A CDN, or Content Delivery Network, is a globally distributed network of servers designed to deliver web content to users quickly and efficiently.

See Crowd-Sourced Change Detection.

Chrome Developer Tools (often called DevTools) is a suite of web authoring and debugging tools built directly into the Google Chrome browser.

This refers to A/B tests that are executed by JavaScript running in the user's browser. The browser first loads the original page, and then a script modifies the page to show a test variation.

Client-Side Rendering is an architectural approach where the server sends a minimal, often empty, HTML shell to the browser.

Cloaking is a deceptive SEO technique where a website shows different content or URLs to search engine crawlers (like Googlebot) than it does to human users.

Connection Type is a RUM metric that identifies the type of network a user is on, such as Wi-Fi, 4G, or Ethernet. This data is valuable for segmenting performance reports to understand how a site p…

CSP is a web security standard that helps prevent common attacks like cross-site scripting (XSS) and data injection. It works by allowing a website to define a whitelist of trusted domains from whi…

The conversion rate is a key business and marketing metric that measures the percentage of website visitors who complete a desired action (a "conversion").

Core Web Vitals are a set of specific, user-centric metrics created by Google to measure the real-world user experience of a webpage.

CORS is a browser security feature that uses HTTP headers to manage whether a web page from one domain is allowed to fetch resources from another domain.

CPU time is the amount of time the Central Processing Unit (CPU) of a user's device spends processing the scripts and rendering a webpage.

Crawl Budget is an SEO term that refers to the number of pages Googlebot will crawl on a website within a given timeframe. For large e-commerce sites, preserving this budget is important.

The critical rendering path is the sequence of steps a browser must take to process the HTML, CSS, and JavaScript files required to render the initial, above the fold view of a webpage.

The crossorigin attribute is an HTML attribute used on elements like script, link, and img when they load a resource from a different domain.

Crowd-Sourced Change Detection is a Web Vitals Monitoring feature that detects performance regressions by comparing a website's current performance against baseline data from its most engaged users…

CrUX is a massive public dataset from Google containing performance data collected from millions of real Chrome users worldwide.

Cumulative Layout Shift (CLS) is one of Google's Core Web Vitals that measures visual stability. It quantifies unexpected layout shifts of visible page elements.

A custom configuration is a setup for Speed Kit that is tailored specifically for your website by our expert Product Integration team.

A custom performance metric is a user-defined measurement used to track the performance of specific, business-critical elements or interactions that are not captured by standard metrics.

Customer Acquisition Cost (CAC) is a key business metric that represents the total cost a company spends to acquire a new customer.

Deferred JS loading is a technique for loading JavaScript files in a non-blocking way using the `defer` attribute on a `<script>` tag.

A deployment is the process of releasing new code, features, or content updates to a live production website. This is a critical event for any caching system, as the cached content may become instantly outdated.

This is an automatic Speed Kit mechanism that detects when a major update or new version of your website has been released (a "deployment").

Device Memory is a RUM metric that reports the amount of RAM on a user's device (e.g., 4GB, 8GB). This allows you to analyze performance for users on high-end devices versus those on low-memory dev…

The Device Pixel Ratio indicates the density of pixels on a device's screen. High-resolution displays (like Apple's "Retina" screens) have a DPR of 2 or more, meaning they use a 2x2 grid of physica…

A 2x DPR Cap is a best practice in Image Optimization for handling high-resolution "Retina" screens. It involves limiting the resolution of images served to these screens to a maximum of twice the CSS pixel size.

Dictionary compression is an advanced compression technique where a shared "dictionary" of common data patterns is used to compress multiple files more efficiently than compressing each one individually.

dns-prefetch is a resource hint (``) that instructs the browser to perform only the DNS lookup for a specific domain in the background.

The DOM is a tree-like representation of all the elements in an HTML document that is created by the browser when it loads a page.

DOM Content Loaded (DOMContentLoaded or DCL) is a browser event that fires when the initial HTML document has been completely loaded and parsed, without waiting for stylesheets, images, and subframes to finish loading.

DOM Size refers to the total number of elements (nodes) and the complexity of their nesting within a page's HTML structure.

Domain Coalescing is an optimization technique where resources that would normally be loaded from multiple different domains are instead consolidated and loaded from a single domain.

Dynamic Blocks are specific, designated areas within a webpage that contain personalized or frequently changing content. Speed Kit can be configured to treat these blocks differently from the rest of the page.

Dynamic caching is Speed Kit's core technology that makes it possible to cache website content that is traditionally considered "uncacheable" because it is personalized or changes frequently (e.g.…

Dynamic Content Merging is a Speed Kit feature that optimizes the delivery of pages with both static and dynamic content. It merges these two parts together in a smart way so that: (1) users get a…

The Dynamic Fetcher is a Speed Kit component that handles the async fetching of dynamic (personalized/session-based) content from the origin server.

Dynamic HTML refers to HTML pages that contain both static content and dynamic content. For example, an e-commerce product page might have a static layout and product description (static) but a dyn…

Early Hints (HTTP 103 response status) is a mechanism that allows the server to send resource hints to the browser before the final HTML response is ready.

The Edge Cache is Fastly's distributed edge caching infrastructure that serves cached content from Fastly's Points of Presence (PoPs) around the world.

Element Timing is a browser API that allows you to measure when specific elements on a page are rendered. This is particularly useful for creating custom performance metrics when Google's standard…

This is a browser API that allows developers to measure the precise render time of specific, designated elements on a page.

An ETag (entity tag) is an HTTP header that serves as a unique identifier for a specific version of a resource. It is a crucial mechanism for efficient cache validation.

EXIF is metadata embedded within image files (like JPEGs) that contains information such as the camera settings, date, time, and sometimes GPS location where the photo was taken.

A fail-safe mechanism is a core architectural principle of Speed Kit that guarantees the service will never slow down a website.

The fetchpriority="high" attribute is an HTML attribute that tells the browser to prioritize loading a specific resource (like an image or script) higher than other resources of the same type.

Field data is performance data collected from the real users visiting your website in their actual environments. It captures the true user experience across the full spectrum of devices, network co…

First Contentful Paint (FCP) is a performance metric that measures the time from when a user initiates loading the page until the first piece of content (text, image, or other element) is rendered on the screen.

See Flicker Effect.

Also known as Flash of Original Content (FOOC), this is a negative user experience that often occurs with Client-Side A/B Testing.

In web performance context, a "frame" is a single rendered snapshot of a webpage. The browser renders frames at a target rate (typically 60 frames per second, or 60 FPS).

frontend refers to the client-side part of a web application that a user directly sees and interacts with in their browser.

Fully Loaded is a synthetic metric that measures the time it takes for a page and all of its resources—including scripts and images—to completely stop loading.

Google Search Console is a free service provided by Google that helps you monitor, maintain, and troubleshoot your website's presence in Google Search results.

Googlebot is the official name for the web crawling bot that Google uses to discover, render, and index pages for its search engine. Speed Kit is designed to be fully compatible with Googlebot.

Guards are configurable "finish line markers" that Speed Kit uses for pages that rely on Client-Side Rendering (CSR). On these pages, it can be difficult to determine when the main content has actu…

gzip is a widely supported and common compression algorithm used by web servers to reduce the file size of text-based assets like HTML, CSS, and JavaScript.

A HAR (HTTP Archive format) file is a JSON-formatted log of a web browser's interaction with a site. It contains a detailed, timestamped record of every single network request and response, includi…

A hard navigation is a traditional page load. When a user clicks a link or types a URL in the address bar, the browser discards the current page and makes a full request to the server for a new HTML document.

A headless browser is a web browser that operates without a graphical user interface (GUI). It runs on a server and can be controlled programmatically.

The amount of data (in bytes) that comprises the HTML document sent from the server to the browser. This includes the HTML markup but excludes CSS, JavaScript, images, and other resources.

This is a sophisticated programming technique used by Speed Kit's algorithm to accurately measure the Largest Contentful Paint (LCP) on complex, JavaScript-heavy sites.

HTTP/2 is a major version of the HTTP protocol designed to make websites faster and more efficient. Its key feature is multiplexing, which allows a browser to download multiple resources (like CSS…

HTTP/3 is the latest version of the HTTP protocol, engineered for even greater performance, especially on unreliable networks. It is built on a new transport protocol called QUIC instead of TCP.

This indicates that the Service Worker API, which is the core browser technology that powers Speed Kit, can only be used on websites that are served securely over HTTPS.

A technique used to add interactivity to server-side rendered (SSR) content by attaching JavaScript event handlers to the existing HTML on the client-side.

This is an automated process Speed Kit uses to make image files as small as possible without sacrificing visual quality, which is crucial for fast loading times.

Instant Loading is a Speed Kit feature that caches the main HTML document and serves it instantly from the cache on subsequent visits, eliminating cold start delays.

Interaction to Next Paint (INP) is a Core Web Vital metric that measures responsiveness. INP measures the time from when a user interacts with the page (like a click or keypress) until the next vis…

Interaction to Next Paint Subpart timings breaks down the three components of INP: Input Delay (inputDelay): The time from when the user interacts until event listeners start to run.

This is a browser API that efficiently detects when an element enters or leaves the screen's viewport. It is one of the tools Speed Kit uses in its algorithm to accurately measure the Largest Conte…

IP whitelisting is a security practice where a server or firewall is configured to grant access only to a specific list of trusted IP addresses.

Lab data is performance data collected in a controlled, repeatable environment using tools like Google Lighthouse or WebPageTest.

A Core Web Vital that measures the perceived loading speed of a page. It marks the point in time when the largest content element (usually a hero image or a large block of text) becomes visible within the viewport.

The LCP Subparts are the distinct phases that make up the total Largest Contentful Paint time. Analyzing this breakdown is crucial for diagnosing the root cause of a slow LCP.

Layout Thrashing is a harmful performance anti-pattern.

Lazy loading is an optimization strategy where content that is not immediately visible to the user—typically images and videos "below the fold"—is deferred and only loaded as the user scrolls down…

In the context of Predictive Preloads, lead time is the "head start" the browser gets to prepare the next page. It is the duration between when Speed Kit's Prediction Engine anticipates a user's ne…

Lighthouse is an open-source, automated tool from Google for auditing the quality of web pages. It runs a series of tests against a page and generates a report with scores for performance, accessib…

The Long Animation Frames (LoAF) API is a modern browser API designed to diagnose responsiveness issues. It provides detailed attribution for slow UI updates (known as "long frames"), helping devel…

A long task is any piece of JavaScript code that monopolizes the Main Thread for a prolonged period (typically over 50 milliseconds), preventing it from responding to user input.

Low-entropy images are images that contain large areas of uniform color, simple gradients, or repeating patterns, such as logos or simple graphics.

These are the algorithms that power Speed Kit's Prediction Engine. They are trained on billions of anonymous user interactions collected from our Real User Monitoring (RUM) system to identify patte…

The main thread is the primary "workspace" within a web browser where it performs most of the work required to display a webpage.

This is part of Speed Kit's Image Optimization process. It involves automatically stripping non-essential, invisible data (metadata) from image files.

A Multi-Page Application is a traditional website architecture where each distinct page is a separate HTML document. Every navigation from one page to another involves a full page reload (Hard Navi…

This is a potential issue that can occur when Speed Kit is used to accelerate a WKWebView inside a native mobile application.

Navigation Type is a RUM metric that indicates how a user arrived at a page. Common types include Maps (e.g., clicking a link), reload, and back_forward (using the browser's back/forward buttons).

Network, in the context of web performance, refers to the series of networks (including the local network, internet service providers, and backbone networks) that connect a user's browser to a website's server.

Network Time is the "travel time" it takes for data to move between a user's browser and a website's server. This is influenced by factors like the physical distance between the user and the server…

This is a specific technical configuration required to enable the Service Worker API within an iOS WKWebView. The app developer must set this property on the WKWebViewConfiguration.

The origin server is the primary "home base" for a website. It is the computer or server cluster where the website's original application code, databases, and assets are hosted.

Origin trials are a framework used by browser vendors to safely test new, experimental web platform features on live websites with real users.

In statistics and A/B testing, a p-value indicates the probability that test results occurred by chance alone. A p-value of 0.05 or lower generally indicates statistical significance, meaning the d…

The p75, or 75th percentile, is a statistical measure representing the point at which 75% of a group of values fall at or below.

Page Load refers to the entire process of a webpage becoming visible and interactive for a user, from the initial navigation request to the final rendering of content.

Page Views is a metric that counts the total number of times a page on a website has been loaded or viewed by users. It is a fundamental measure of traffic and engagement.

PageSpeed Insights is a free tool from Google that analyzes the performance of a single webpage and provides suggestions for improvement.

Passthrough Mode is a temporary, protective state that Speed Kit enters when its Deployment Detection mechanism identifies a major website update.

performance.mark() is a method from the browser's User Timing API that allows a developer to programmatically create a named timestamp at a specific point in their JavaScript code.

performance.measure() is a method from the browser's User Timing API. It is used to calculate the time elapsed between two performance.mark() timestamps, creating a custom performance measurement.

This is a scheduled, time-based mechanism that Speed Kit uses to keep its cache fresh. It can be configured to automatically re-check and update specific pages or assets at regular intervals (e.g.…

Personalization is the practice of tailoring website content to individual users based on their data, such as past behavior, location, or user profile.

A placeholder is a temporary visual element, such as a loading spinner or a gray "skeleton" box, that is displayed on a page while the final content is being loaded in the background.

Pogo-sticking is a user behavior that sends a negative signal to search engines. It occurs when a user clicks on a search result, finds the page unsatisfactory (often because it's too slow to load)…

A polyfill is a piece of code that provides modern functionality on older browsers that do not natively support it. Developers use polyfills to allow them to write modern JavaScript while still mai…

Pre-caching is the first step in Speed Kit's Predictive Preloads feature. Once the Prediction Engine identifies a likely next page for a user, the Service Worker proactively fetches the HTML for th…

Pre-rendering is the final and most powerful step of Predictive Preloads. After a page's HTML has been pre-cached, the browser can use modern technologies like the Speculation Rules API to fully re…

Pre-warming the cache is the proactive process of populating a cache with content before any user requests it. After a cache is purged (for example, following a deployment), Speed Kit's system uses…

Preconnect is a resource hint (``) that tells the browser to establish an early connection to a third-party domain. It performs the necessary DNS lookup, TCP handshake, and TLS negotiation in the b…

The Prediction Engine is the "brain" behind Speed Kit's Predictive Preloads. It is a sophisticated system built on Machine Learning Models that analyzes real-time user behavior (like mouse movement…

Predictive Preloads is an advanced Speed Kit feature designed to make website navigation feel instantaneous. It uses a Prediction Engine to anticipate where a user will go next.

Prefetch is a resource hint (``) that tells a browser to fetch a resource with low priority because it might be needed for a future navigation.

Preload is a resource hint (`) used in the HTML ` to instruct the browser to download a critical resource for the current page with high priority, before it would be discovered naturally.

A Progressive Web App is a modern website that is designed to offer an app-like experience. By leveraging web technologies, especially the Service Worker, a PWA can provide features traditionally a…

Quality Score is a diagnostic metric used by Google Ads to estimate the quality of your ads, keywords, and landing pages. A higher Quality Score can lead to lower ad prices and better ad positions.

QUIC is a modern transport layer network protocol that serves as the foundation for HTTP/3. It is designed for speed and is built on top of UDP instead of TCP.

See Field Data.

A redirect is a response from a server that automatically forwards a user from one URL to another. While sometimes necessary (e.g., for tracking or moving content), redirects are very harmful to performance.

This is a browser API that tells the browser to execute a function just before the next screen repaint, which is ideal for running smooth animations and visual updates.

Response time limits are the established psychological thresholds that dictate how users perceive system delays. Research shows there are critical boundaries for user attention and patience: intera…

Responsive Design is an approach to web development that ensures a site's layout and content adapt to provide an optimal experience on any device, from mobile phones to large desktop monitors.

ROI is a business metric used to evaluate the profitability of an investment by comparing the net profit to the cost of the investment. It is typically expressed as a percentage.

RTT stands for Round Trip Time and is a fundamental networking metric. It measures the total time it takes for a data packet to travel from a source (like a user's browser) to a destination (a serv…

0-RTT (Zero Round-Trip Time Resumption) is a high-performance feature of modern network protocols like TLS 1.3 and HTTP/3.

SEO is the process of improving a website's visibility in search engine results pages (like Google). The goal is to rank higher than competitors for relevant search queries to attract more organic (free) traffic.

Server Response Time is a component of Time to First Byte that measures how long the server takes to process a request and start sending back a response, excluding network latency.

Server Timing is a browser API that allows the backend to communicate performance metrics about its own internal processes (e.g., database query time, time to render a component) to the browser via HTTP headers.

This is a performance-friendly method for running A/B tests. Unlike Client-Side A/B Testing, the decision of which variation to show a user is made on the Origin Server.

Server-Side Rendering is an architectural approach where the server generates the full HTML for a page before sending it to the browser. The browser receives a complete document that it can start rendering immediately.

A service worker is a script that runs in the background in a user's web browser, separate from the web page. It acts as a programmable network proxy, giving a website the ability to intercept and…

This is the fastest cache available. It is a storage space directly inside the user's web browser that is controlled by the Service Worker.

The Service Worker Lifecycle refers to the sequence of states a Service Worker goes through from its initial registration to becoming active.

Session Length is a RUM metric that measures the total duration of a user's visit to a website, from their first page view to their last.

A session is a group of interactions that one user takes on your website within a given timeframe. A single session can include multiple Page Views, clicks, and other events.

The Shadow DOM is a browser feature that allows developers to create a hidden, encapsulated DOM tree within a normal element. This "shadow" tree's styles and scripts are isolated from the main page.

The Shopify App Store is the official marketplace where Shopify merchants can find and install third-party applications to add new features and functionality to their e-commerce stores.

A Single-Page Application (SPA) is a modern web application that loads a single HTML page and then dynamically updates the content as the user interacts with it, offering a fluid, app-like user experience.

A soft navigation occurs in a Single-Page Application (SPA) when a user clicks a link and the content of the page changes without a full page reload (Hard Navigation).

This is a modern browser API that allows a website to declaratively tell the browser which pages a user is likely to navigate to next.

Speed Guards are a feature of Speed Kit's Real User Monitoring (RUM) tool. They function as an automated anomaly detection system that continuously analyzes your performance data in near real-time.

The Speed Impact Chart is a data visualization and analysis method used by Speed Kit to prove the business value of web performance.

Speed Index is a lab-based performance metric that measures how quickly the visual content of a page is populated during the page load.

The Speed Kit Dashboard is the web-based control center for your Speed Kit configuration. It provides a user-friendly interface where you can view which assets are in the cache, manually trigger co…

This refers to the specific Speed Kit documentation that provides a detailed overview of our integrated Real User Monitoring (RUM) solution.

This refers to the specific Speed Kit documentation that explains and quantifies how improving web performance directly drives positive business outcomes.

Start Render is a lab metric that marks the point in time when the very first pixels are painted to the user's screen. It is essentially the same as First Contentful Paint (FCP), representing the f…

Statistical significance is a conclusion reached in an A/B test when the data shows that the observed result is very unlikely to have occurred due to random chance. It is typically determined by calculating a p-value.

Synthetic monitoring is the methodology of collecting performance data from a simulated, controlled environment. It is the same as Lab Data and uses tools like Lighthouse or WebPageTest to run repe…

A tag manager (like Google Tag Manager) is a system that allows marketing and business teams to add and manage third-party marketing tags (snippets of code for analytics, advertising, etc.) on a we…

A third-party script or tool is any piece of code, functionality, or service that is provided by an external vendor and integrated into a website.

Throttling is a technique used in Lab Data tools (like Lighthouse) to simulate how a website would perform on slower devices or less reliable network connections.

A foundational web performance metric measuring the time from when a user makes a request to when their browser receives the very first byte of the HTML response.

Time to Interactive is a performance metric that measures the time it takes for a page to become fully and reliably responsive to user input.

Time-to-Live is a setting for a piece of content in a cache that specifies how long it should be considered "fresh." After the TTL expires, the caching system knows it must re-validate the content…

Total Blocking Time is a lab metric that measures the total amount of time between First Contentful Paint (FCP) and Time to Interactive (TTI) where the Main Thread was blocked by a Long Task.

trace.cafe is a web-based performance trace viewer. It allows developers to upload and analyze detailed performance trace files (e.g., from Lighthouse or Chrome DevTools) to perform in-depth debugg…

A URL parameter (also known as a query string) is the part of a URL that follows a question mark (?), used to pass data to the server (e.g., ?utm_source=google).

User Experience (UX) is the overall perception and feeling a person has when interacting with a product, system, or service, such as a website.

User Timing is a browser API that allows developers to create custom, application-specific timestamps in their code to measure the performance of certain operations.

The viewport is the user's visible area of a webpage on their device's screen. Its size and dimensions vary depending on the device (mobile phone, desktop, etc.).

Visually Complete is a lab metric that marks the point in time when all the content in the visible, above the fold portion of the page has finished rendering.

A waterfall chart is a type of data visualization used in web performance analysis tools to illustrate how a browser loads all the assets on a webpage.

Web fonts are fonts that are downloaded by the browser on demand to render text in a specific typeface that is not pre-installed on the user's device.

A web performance budget is a set of defined limits for key performance metrics that a website is not allowed to exceed. Rather than focusing on simple metrics like file size, modern performance bu…

A Web Worker is a script that runs in the background in a browser, on a separate thread from the main UI thread. This allows you to perform computationally intensive tasks without freezing or block…

WebP is a modern image format developed by Google that offers superior compression and smaller file sizes compared to older formats like JPEG and PNG.

WebPageTest is an advanced, open-source tool used for in-depth performance analysis. It provides highly detailed Lab Data by running tests from various geographical locations on real devices with s…

A WKWebView is the modern browser component that native iOS applications use to display web content directly inside the app. Think of it as a mini-browser window embedded within an app's interface.

This is the "settings panel" for a WKWebView. It is a configuration object that an iOS app developer uses to set up the properties and behavior of the in-app browser view.