PERFORMANCE · SEO GLOSSARY
Site Speed
How quickly a web page loads and becomes interactive — a confirmed Google ranking factor since 2010 for desktop (2018 for mobile). Measured by Core Web Vitals (LCP, INP, CLS) in the field and lab metrics (TTFB, FCP, TTI) in synthetic testing.
Definition
Site speed encompasses how quickly a page delivers its content to users. Google formally uses Core Web Vitals (CWV) as ranking signals: LCP (Largest Contentful Paint — how fast the main visible content loads, target <2.5s), INP (Interaction to Next Paint — responsiveness to user interactions, target <200ms), and CLS (Cumulative Layout Shift — visual stability during load, target <0.1). These are measured from real Chrome users via the Chrome User Experience Report (CrUX) in a 28-day rolling window — this is field data, as opposed to lab data from tools like Lighthouse. Related lab metrics: TTFB (Time to First Byte — server response speed), FCP (First Contentful Paint — first pixel rendered), and TTI (Time to Interactive — when JavaScript finishes executing). Site speed affects SEO through two channels: (1) direct CWV ranking signals; (2) bounce rate and engagement signals — slow pages have higher abandonment rates, which may indirectly affect rankings through engagement-quality signals.
Why it matters for SEO
Core Web Vitals are an official Google ranking signal for all searches since 2021. The LCP threshold is the most impactful: pages in the "Poor" range (>4s LCP) are disadvantaged in rankings compared to competitors with equivalent content in the "Good" range (<2.5s). On mobile, where LCP is typically worse (slower CPUs, variable network), the impact is more pronounced. Improving LCP from Poor to Good on key landing pages is often the highest-ROI technical SEO improvement for sites that fail CWV.
How DeepSEOAnalysis checks this
The audit uses real CrUX field data for LCP, INP, and CLS — segmented by mobile and desktop — for the crawled domain. Each metric is scored against the Good/Needs Improvement/Poor thresholds and linked to specific fix recommendations (LCP: image optimisation, fetchpriority, preload; INP: main thread task optimisation, defer JS; CLS: width/height on images, avoid dynamic ad units).
Useful tools and resources
GLOSSARY
Related terms
performance
Core Web Vitals
Three Google metrics — LCP, INP, and CLS — that measure real-user loading, interactivity, and visual stability.
Read definition →performance
Page Speed
The time it takes for a page to load and become usable — measured by multiple metrics including TTFB, FCP, and Core Web Vitals.
Read definition →performance
First Contentful Paint (FCP)
A performance metric measuring the time from page navigation start until the browser renders the first piece of content — text, image, or SVG — on screen. FCP is not a Core Web Vital but is a useful early-load diagnostic.
Read definition →performance
Total Blocking Time (TBT)
A Lighthouse lab metric measuring the total time the main thread is blocked by long tasks between First Contentful Paint and Time to Interactive — a proxy for interactivity that correlates with INP in the field.
Read definition →See how your site scores on Site Speed.
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