--- title: Core Web Vitals Monitoring: LCP, CLS & TBT description: Core Web Vitals monitoring by WatchFor. Load your pages in a real headless Chromium browser on a schedule, measure LCP, CLS, FCP, TBT and Speed Index, and get alerted when performance regresses before it hurts your SEO and conversions. canonical: https://watchfor.io/core-web-vitals-monitoring --- # Core Web Vitals Monitoring for Real-World Page Speed Catch a Core Web Vitals regression before it costs you rankings. WatchFor loads your pages in a real Chromium browser and runs a Lighthouse audit on a schedule. [Get started for free](/auth/sign-up)[View pricing](/pricing) [Part of synthetic monitoring: API, browser and Core Web Vitals checks](/synthetic-monitoring) ## Comprehensive Core Web Vitals Monitoring Features Everything you need to keep your pages fast and stable ### Real Browser Rendering Every check runs in a headless Chromium browser that downloads, parses, and renders your page the same way a real user's browser would — not a simple HTTP request. ### Largest Contentful Paint Track LCP to see how quickly your main content becomes visible. Spot slow images, render-blocking resources, and server delays that make pages feel sluggish. ### Cumulative Layout Shift Measure CLS to catch unstable layouts that jump as the page loads. Identify late-loading ads, images, and fonts that frustrate users and trigger misclicks. ### Responsiveness (Total Blocking Time) Track TBT, the lab stand-in for Interaction to Next Paint, to surface heavy JavaScript and main-thread blocking that makes interactions lag. INP itself needs real-user data, so no synthetic check can measure it — we say so instead of inventing a number. ### Full Performance Profile Beyond the Core Web Vitals, every audit also records FCP, TBT, Time to Interactive, Speed Index and the Lighthouse category scores, giving you a complete picture of where the loading experience slows down. ### Threshold Alerting New monitors alert on LCP over 4 s and CLS over 0.25; tighten them or add performance and SEO score rules. Audits aren't re-run early, so by default a rule fires after 3 audits in a row past the line (you can set it to 1). ### Performance Trends Review each Core Web Vital over time with clear graphs, perfect for spotting slow regressions, validating optimizations, and proving the impact of your work. ### Scheduled Audits Run PageSpeed-style audits on a recurring schedule, from once an hour to once a day, plus maintenance windows so deploys and planned work never trigger alerts. ## A closer look Lighthouse scores, a screenshot of the tested page, and its LCP and CLS. Score and Web Vitals trends, plus the fixes that save the most time. Alert on LCP and CLS at the web.dev thresholds, as warning or critical. ## Why Choose Our Core Web Vitals Monitoring? Page speed is no longer a nice-to-have — Core Web Vitals are a direct Google ranking factor and a proven driver of bounce rate and conversions. A one-off PageSpeed score tells you nothing about how your site performs tomorrow, after the next deploy, or once a third-party script slows down. Our monitor runs a real-browser audit on a schedule so you have a continuous, trustworthy record of LCP, CLS, TBT and your Lighthouse scores. When LCP, CLS or a score stays past your threshold, you hear about it after a few audits — long before Google's field data catches up. [Start monitoring now](/auth/sign-up) Real headless Chromium rendering, not synthetic estimates Track LCP, CLS, FCP, TBT, Speed Index and Lighthouse scores Catch performance regressions right after a deploy Spot slow or failing third-party scripts early Protect SEO rankings and conversion rates Historical trend graphs for every metric Configurable thresholds and audit intervals Alerts via email, Slack, Discord and 13 more channels ## How Core Web Vitals Monitoring Works Simple setup, real performance visibility 1 ### Add Your Page Enter the URL you want to audit. Choose the pages that matter most — your landing page, checkout, or any high-traffic route. 2 ### Set Thresholds Pick the metrics you care about and the limits that define good performance, such as LCP under 2.5s or CLS under 0.1. 3 ### Audit on a Schedule A real Chromium browser loads your page at your chosen interval, recording LCP, CLS, FCP, TBT, Speed Index and the Lighthouse scores on every run. 4 ### Get Alerted on Regressions When a metric stays past your threshold for the number of audits you set (3 by default), you get a notification and a timeline showing when performance changed. ## Core Web Vitals Monitoring Use Cases Perfect for any page where speed and stability matter ### Protecting SEO Rankings Core Web Vitals feed directly into Google's page experience signals. Continuous monitoring ensures a slow regression never quietly erodes your search visibility and organic traffic. ### Catching Deploy Regressions A new feature, image, or library can tank your metrics overnight. Scheduled audits show the audit where performance dropped, so you can tie it to the release that caused it. ### Watching Third-Party Scripts Analytics, ad tags, chat widgets, and A/B tools all run in the same browser as your page. Real-browser audits reveal when a third party starts slowing down LCP or blocking the main thread. ### Safeguarding Conversions Every extra second of load time and every layout shift costs you customers on key pages. Keep checkout, signup, and product pages fast to protect revenue and user trust. ## Frequently asked questions Everything you need to know about Core Web Vitals monitoring [All questions→](/faq)[Ask us directly](/contact) What are Core Web Vitals? Core Web Vitals are a set of Google metrics that measure the real-world experience of loading a web page. The three current vitals are Largest Contentful Paint (loading speed), Cumulative Layout Shift (visual stability) and Interaction to Next Paint (responsiveness). Google uses them as a ranking signal, so keeping them healthy matters for both users and SEO. How is this different from a one-off PageSpeed test? Do you measure in a real browser? Which metrics do you track? Mobile or desktop? How often are audits run? Can I get alerted when a metric gets worse? Why do Core Web Vitals affect SEO? Can I monitor pages behind a login or that are private? Which plans include Core Web Vitals monitoring? ## From our blog Guides, deep-dives, and best practices from the WatchFor team [Performance ### Core Web Vitals Explained: LCP, CLS, INP (and how to keep them green) Jun 19, 2026·4 min readRead article](/blog/core-web-vitals-explained)[Performance ### LCP Explained: Largest Contentful Paint (and how to improve it) Jan 29, 2026·3 min readRead article](/blog/lcp-explained)[Performance ### CLS Explained: Cumulative Layout Shift (and how to fix it) Jan 27, 2026·3 min readRead article](/blog/cls-explained) ## Ready to Keep Your Pages Fast with Core Web Vitals Monitoring? Core Web Vitals monitoring is included from the Pro plan. Want to see where a page stands first? The free Core Web Vitals checker runs a one-off audit with no signup. [Get started for free](/auth/sign-up)[View documentation](/docs/monitors/performance#core-web-vitals-browser) --- Canonical page: https://watchfor.io/core-web-vitals-monitoring · Site guide: https://watchfor.io/llms.txt