PERFORMANCE · SEO GLOSSARY
Core Web Vitals
Google\'s three user-experience metrics — Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and Interaction to Next Paint (INP) — measured at the p75 threshold from real Chrome user field data (CrUX), used as a Page Experience ranking signal in Google Search.
Definition
Core Web Vitals (CWV) are three metrics Google has defined as the most important user-experience signals for web pages, measured from real Chrome user field data collected in the Chrome User Experience Report (CrUX): (1) **Largest Contentful Paint (LCP)**: the render time of the largest visible content element in the initial viewport (typically the hero image or headline). Measures perceived load speed. Target: ≤2.5s. Poor: >4s. (2) **Cumulative Layout Shift (CLS)**: the sum of unexpected layout shifts during the page\'s lifetime (weighted by shift fraction × impact fraction). Measures visual stability. Target: ≤0.1. Poor: >0.25. (3) **Interaction to Next Paint (INP)**: the latency from a user interaction (click, tap, or keypress) to when the browser renders the next frame in response. Measures interactivity. Target: ≤200ms. Poor: >500ms. INP replaced First Input Delay (FID) as the third Core Web Vital in March 2024. How CWV affects SEO: Core Web Vitals are a confirmed Google ranking signal (Page Experience signal), which Google confirmed in 2021 and has updated annually. Google evaluates pages at the p75 threshold from CrUX field data — meaning 75% of real user sessions must achieve the target threshold for the page to pass. Pages with all three metrics in the "Good" range pass; any metric in "Poor" fails. CrUX field data requirements: pages must have sufficient Chrome user traffic to have CrUX data — low-traffic pages may not have URL-level data (Google uses domain-level data as a fallback). Pages without CrUX data are not penalised but also do not benefit from positive CWV signals. Where to check: Google Search Console (Core Web Vitals report, Page Experience report), PageSpeed Insights (combines CrUX and Lighthouse data), and DeepSEOAnalysis (CrUX p75 data for each metric per URL).
Why it matters for SEO
Core Web Vitals are Google\'s primary quantitative page experience ranking signals — the only performance metrics Google has confirmed as direct ranking factors. Poor CWV (particularly LCP >4s, which is common for image-heavy pages with unoptimised hero images) can suppress rankings regardless of content quality. For competitive queries where multiple pages have similar content quality, CWV can be the differentiating signal. Beyond rankings, CWV correlates with user abandonment: high LCP causes users to leave before the page loads; high CLS causes accidental clicks; high INP makes interactions feel unresponsive.
How DeepSEOAnalysis checks this
DeepSEOAnalysis fetches real CrUX field data at p75 for every audited URL, reporting LCP, CLS, and INP from actual Chrome users (not Lighthouse lab scores or synthetic tests). This is the same data Google uses for ranking assessment. We also report whether each metric is in the Good/Needs Improvement/Poor band and identify specific technical causes: LCP element identification, render-blocking resources, images without dimension attributes (CLS), and third-party script timing (INP).
GLOSSARY
Related terms
performance
LCP Image
The image element identified by Chrome as the Largest Contentful Paint (LCP) candidate on a page — the largest visible image in the initial viewport that determines the LCP timing score, typically the hero image, product thumbnail, or featured photo at the top of the page.
Read definition →performance
CLS Reserve (Layout Shift Reserve)
A front-end technique that pre-allocates fixed space for elements that load asynchronously (ads, images without dimensions, embedded iframes) using CSS aspect-ratio, min-height, or explicit width/height attributes — preventing the layout shift those elements would otherwise cause when they load and displace surrounding content.
Read definition →performance
Render-Blocking Resources (SEO)
CSS stylesheets and JavaScript files that block the browser from rendering page content until they are downloaded and processed — a primary cause of poor LCP and FCP (First Contentful Paint) scores, requiring deferral, async loading, or inline critical CSS strategies to resolve.
Read definition →performance
font-display (SEO)
The CSS `font-display` descriptor that controls how a browser handles text rendering while a web font is loading — affecting both the Cumulative Layout Shift (CLS) metric (from font swap reflow) and the First Contentful Paint (FCP) timing (from invisible text during font loading).
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Lazy Loading SEO
The SEO implications of lazy loading — deferring loading of images and other resources until they enter the viewport — which improves initial page load performance but can harm LCP if the main content image is lazy-loaded, and can prevent off-screen content from being indexed if text content is lazy-loaded.
Read definition →See how your site scores on Core Web Vitals.
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