# Glossary A reference guide to terminology used in VitalSentinel and web performance monitoring. *** ## A [#a] ### Accessibility Score [#accessibility-score] A Lighthouse metric (0-100) measuring how accessible your website is to users with disabilities, including screen reader compatibility, color contrast, and keyboard navigation. ### Alert [#alert] A notification triggered when a monitored metric exceeds a defined threshold. Alerts can be Warning (potential issue) or Critical (urgent problem). See [Setting Up Alerts](/alerts/setting-up-alerts). *** ## B [#b] ### Best Practices Score [#best-practices-score] A Lighthouse metric (0-100) measuring adherence to web development best practices including HTTPS usage, no console errors, and correct image aspect ratios. ### Bounce Rate [#bounce-rate] The percentage of sessions where users leave after viewing only one page without any interaction. *** ## C [#c] ### CDN (Content Delivery Network) [#cdn-content-delivery-network] A network of distributed servers that deliver content to users from geographically closer locations, improving load times and reducing TTFB. ### Consent [#consent] User permission for data collection. VitalSentinel's default storage mode uses no cookies and stores nothing on the visitor's device. Both the session and persistent storage modes store an identifier on the visitor's device, and you must obtain your visitors' consent before you enable either. See [Data & Privacy](/others/data-privacy). ### CORS (Cross-Origin Resource Sharing) [#cors-cross-origin-resource-sharing] A security mechanism that controls how web pages can request resources from different domains. CORS errors can cause resource loading failures. ### CLS (Cumulative Layout Shift) [#cls-cumulative-layout-shift] A Core Web Vital measuring visual stability. It quantifies how much the page layout shifts unexpectedly during loading. Good: ≤ 0.1. ### Core Web Vitals [#core-web-vitals] Google's key metrics for measuring user experience: LCP (loading), INP (interactivity), and CLS (visual stability). These affect search ranking. See [RUM Monitoring](/features/rum-monitoring) and [CrUX Monitoring](/features/crux-monitoring). ### CrUX (Chrome User Experience Report) [#crux-chrome-user-experience-report] A public dataset from Google containing real-world performance data from Chrome users who opt into sharing statistics. Updated monthly. See [CrUX Monitoring](/features/crux-monitoring). ### Crawlability [#crawlability] The ability of search engine bots to access and index your website pages. *** ## D [#d] ### DNS Lookup [#dns-lookup] The process of converting a domain name to an IP address. Slow DNS can increase TTFB. ### Domain [#domain] A website address (e.g., example.com) that you add to VitalSentinel for monitoring. Each domain can have its own monitoring configuration. *** ## E [#e] ### E-commerce Tracking [#e-commerce-tracking] Automatic detection and tracking of online store events like product views, cart actions, and purchases. VitalSentinel auto-detects Shopify, WooCommerce, Magento, and Squarespace. See [Web Analytics](/features/web-analytics). ### Engagement Rate [#engagement-rate] The percentage of sessions with meaningful user interaction (scrolling, clicking, or spending significant time on page). See [Engagement Analytics](/features/engagement-analytics). ### Entry Page [#entry-page] The first page a visitor lands on when starting a session. Also called a landing page. ### Error Rate [#error-rate] The percentage of page views that include JavaScript errors. Used for RUM alerts. ### Evaluation Window [#evaluation-window] For Synthetic alerts, the number of recent tests to average when evaluating alert conditions (last 1, 3, 5, or 10 tests). ### Exit Page [#exit-page] The last page a visitor views before ending their session. *** ## F [#f] ### FCP (First Contentful Paint) [#fcp-first-contentful-paint] The time until the first text, image, or canvas element appears on screen. Indicates perceived loading speed. ### Field Data [#field-data] Performance data collected from real users visiting your site (e.g., RUM, CrUX). Compare with Lab Data. ### Form Factor [#form-factor] Device category used for filtering data. CrUX and RUM support Phone, Desktop, and All. Alerts support Phone, Desktop, or Any (all devices). *** ## G [#g] ### GDPR (General Data Protection Regulation) [#gdpr-general-data-protection-regulation] EU privacy regulation governing data collection and processing. VitalSentinel's default storage mode uses no cookies; whether you need a consent banner depends on the storage mode you choose and on your own jurisdiction. See [Data & Privacy](/others/data-privacy). ### GSC (Google Search Console) [#gsc-google-search-console] Google's tool for monitoring search performance and indexing status. VitalSentinel integrates with GSC for indexing and keyword data. See [Google Search Console Integration](/features/google-search-console). ### gTLD (Generic Top-Level Domain) [#gtld-generic-top-level-domain] Common domain extensions like .com, .net, .org. VitalSentinel supports domain expiration monitoring for most gTLDs. *** ## H [#h] ### HTTP Status Code [#http-status-code] A three-digit response code from servers. 2xx = success, 3xx = redirect, 4xx = client error, 5xx = server error. Used in uptime monitoring. *** ## I [#i] ### INP (Interaction to Next Paint) [#inp-interaction-to-next-paint] A Core Web Vital measuring interactivity. It tracks the latency of all user interactions and reports the worst (or near-worst) interaction. Good: ≤ 200ms. ### Incident [#incident] A period when your site is down or unreachable. VitalSentinel tracks incident start time, end time, and duration. ### Indexing [#indexing] The process of search engines adding pages to their database so they can appear in search results. See [Indexing Monitoring](/features/indexing-monitoring). *** ## J [#j] ### JavaScript Error [#javascript-error] A runtime error in browser JavaScript code. VitalSentinel's RUM script automatically captures uncaught exceptions, promise rejections, and console errors. See [Error Tracking](/features/error-tracking). *** ## L [#l] ### Lab Data [#lab-data] Performance data from controlled synthetic tests (e.g., Lighthouse). Consistent but doesn't reflect real user conditions. Compare with Field Data. ### LCP (Largest Contentful Paint) [#lcp-largest-contentful-paint] A Core Web Vital measuring loading performance. It tracks when the largest content element becomes visible. Good: ≤ 2.5s. ### Lighthouse [#lighthouse] Google's open-source tool for auditing web page quality. VitalSentinel uses Lighthouse for Synthetic Monitoring. See [Synthetic Monitoring](/features/synthetic-monitoring). *** ## M [#m] ### Main Thread [#main-thread] The browser's primary execution thread for JavaScript, layout, and rendering. Long tasks on the main thread cause poor INP scores. *** ## N [#n] ### Network Requests [#network-requests] The total number of HTTP requests made when loading a page. A Synthetic monitoring metric – high request counts can slow page load. ### noindex [#noindex] A directive telling search engines not to index a page, using meta tags or HTTP headers. *** ## O [#o] ### Origin [#origin] The combination of protocol, domain, and port (e.g., `https://example.com`). CrUX provides origin-level and URL-level data. *** ## P [#p] ### P75 (75th Percentile) [#p75-75th-percentile] The value that 75% of measurements are equal to or better than. Used by Google for Core Web Vitals assessment. ### Page View [#page-view] A single instance of a page being loaded or viewed. The fundamental unit of web analytics measurement. ### Performance Score [#performance-score] A Lighthouse metric (0-100) summarizing overall page performance, weighted across FCP, SI, LCP, TBT, and CLS. ### PSI (PageSpeed Insights) [#psi-pagespeed-insights] Google's tool that combines Lighthouse testing with CrUX data. VitalSentinel synthetic tests run on PSI infrastructure. *** ## R [#r] ### Referrer [#referrer] The URL of the page that linked to the current page. Used to track traffic sources in Web Analytics. ### Render-Blocking [#render-blocking] Resources (CSS, JavaScript) that prevent the page from rendering until they're fully loaded. A common cause of poor FCP and LCP. ### Response Time [#response-time] The time taken for a server to respond to an HTTP request. Tracked in uptime monitoring. ### Rage Clicks [#rage-clicks] Rapid, frustrated clicking (3+ clicks in 1 second within 100px). Indicates UI issues or unresponsive elements. See [Engagement Analytics](/features/engagement-analytics). ### Rich Results [#rich-results] Enhanced search result formats like FAQs, recipes, or product listings, powered by structured data. ### robots.txt [#robotstxt] A file at your domain root that tells search engines which URLs they can crawl. See [Robots.txt Monitoring](/features/robots-txt-monitoring). ### RUM (Real User Monitoring) [#rum-real-user-monitoring] Collecting performance data from actual website visitors using a tracking script. Provides real-world insights. See [RUM Monitoring](/features/rum-monitoring) and [RUM Script Installation](/installation/rum-script). *** ## S [#s] ### Sample Rate [#sample-rate] The percentage of visitors whose data is collected by RUM. 100% tracks everyone; lower rates reduce data volume while maintaining statistical validity. ### Scroll Depth [#scroll-depth] How far down the page users scroll, measured as percentage milestones (25%, 50%, 75%, 90%, 100%). ### SEO Score [#seo-score] A Lighthouse metric (0-100) measuring search engine optimization factors like meta tags, crawlability, and mobile-friendliness. ### Session [#session] A single visit to your website. A new session starts after 30 minutes of inactivity. ### SI (Speed Index) [#si-speed-index] A Lighthouse metric measuring how quickly content is visually displayed during page load. ### Sitemap [#sitemap] An XML file listing your website's URLs to help search engines discover and crawl your content. ### Soft 404 [#soft-404] A page that looks like an error (thin content, "not found" message) but returns a 200 status code instead of 404. ### SPA (Single Page Application) [#spa-single-page-application] A web app that loads a single HTML page and dynamically updates content. VitalSentinel auto-detects SPA navigation via the History API. ### SSL/TLS [#ssltls] Encryption protocols that secure data between browsers and servers. Indicated by HTTPS and the padlock icon. ### Stack Trace [#stack-trace] A report showing the sequence of function calls that led to an error. Captured by RUM for JavaScript error debugging. ### Synthetic Monitoring [#synthetic-monitoring] Running automated tests from controlled environments to measure performance consistently. Compare with RUM. See [Synthetic Monitoring](/features/synthetic-monitoring). *** ## T [#t] ### Time on Page [#time-on-page] The duration a user spends on a page before navigating away. An engagement metric tracked by RUM. ### TLD (Top-Level Domain) [#tld-top-level-domain] The last part of a domain name (.com, .org, .co.uk). Some TLDs don't support WHOIS lookups for domain expiration monitoring. ### Traffic Source [#traffic-source] How visitors arrive at your site: Direct, Organic Search, Social, Referral, Email, Paid, or AI Search & Tools. ### TBT (Total Blocking Time) [#tbt-total-blocking-time] A Lighthouse metric measuring main thread blocking between FCP and TTI. Used as a lab proxy for INP. ### TTFB (Time to First Byte) [#ttfb-time-to-first-byte] Time from request start until the first byte of response is received. Indicates server responsiveness. ### TTI (Time to Interactive) [#tti-time-to-interactive] The time until the page is fully interactive and responds to user input within 50ms. *** ## U [#u] ### Uptime [#uptime] The percentage of time your website is accessible. 99.9% uptime = \~43 minutes downtime per month. See [Uptime Monitoring](/features/uptime-monitoring). ### URL Inspection [#url-inspection] A Google Search Console feature that checks the indexing status and issues for specific URLs. ### User-agent [#user-agent] In robots.txt, specifies which crawler a rule applies to (e.g., Googlebot, Bingbot, or \* for all crawlers). ### UTM Parameters [#utm-parameters] Tracking codes added to URLs (utm\_source, utm\_medium, utm\_campaign) to track marketing campaign effectiveness. *** ## V [#v] ### Viewport [#viewport] The visible area of a web page. Mobile viewport is smaller than desktop. ### Visitor [#visitor] A person identified by a pseudonymous visitor ID. Different from sessions (one visitor can have multiple sessions). *** ## W [#w] ### Web Vitals [#web-vitals] Google's initiative defining quality metrics for user experience on the web. Core Web Vitals are a subset used for ranking. ### WHOIS [#whois] A protocol for querying domain registration information. VitalSentinel uses WHOIS to monitor domain expiration dates (where available). ### Workspace [#workspace] An organizational container in VitalSentinel that holds domains, team members, and billing. Agencies typically use multiple workspaces for clients. See [Managing Workspaces](/workspace/managing-workspaces).