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Official statement

A single speed metric like the Largest Contentful Paint (LCP) is insufficient. It is also essential to measure interactivity (to avoid unresponsive clicks) and visual stability (to prevent elements from shifting during interaction). Multiple metrics must be combined into a single signal.
🎥 Source video

Extracted from a Google Search Central video

💬 EN 📅 06/05/2021 ✂ 26 statements
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Other statements from this video 25
  1. La vitesse de chargement est-elle vraiment un facteur de classement secondaire ?
  2. Comment Google ajuste-t-il le poids de ses signaux de classement après leur lancement ?
  3. La vitesse d'un site peut-elle compenser un contenu médiocre ?
  4. Pourquoi mesurer uniquement le LCP est-il une erreur stratégique pour votre SEO ?
  5. Comment Google valide-t-il réellement ses signaux de classement avant de les déployer ?
  6. Google distingue-t-il vraiment deux types de changements de classement ?
  7. Pourquoi votre classement Google varie-t-il autant selon la géolocalisation de la requête ?
  8. Pourquoi Google crawle-t-il votre site à une vitesse différente de celle mesurée par vos utilisateurs ?
  9. Pourquoi Google refuse-t-il de divulguer le poids exact de ses facteurs de classement ?
  10. Pourquoi Google utilise-t-il vraiment la vitesse comme facteur de classement ?
  11. Pourquoi Google ne se soucie-t-il pas du spam de vitesse ?
  12. Pourquoi les métriques SEO peuvent-elles signaler une régression alors que l'expérience utilisateur s'améliore ?
  13. La vitesse de chargement mérite-t-elle encore qu'on s'y consacre autant ?
  14. Le HTTPS n'est-il qu'un simple bris d'égalité entre sites équivalents ?
  15. Le HTTPS n'est-il vraiment qu'un « bris d'égalité » dans le classement Google ?
  16. Comment Google détermine-t-il vraiment le poids de chaque signal de classement ?
  17. Pourquoi Google mesure-t-il parfois l'impact d'une mise à jour avec des métriques négatives ?
  18. La vitesse de chargement est-elle vraiment un signal de classement mineur ?
  19. La vitesse du site est-elle vraiment secondaire face à la pertinence du contenu ?
  20. Vitesse de crawl vs vitesse utilisateur : pourquoi Google distingue-t-il ces deux métriques ?
  21. Pourquoi vos résultats de recherche varient-ils selon les régions et langues ?
  22. Votre site est-il vraiment global ou juste multilingue ?
  23. Faut-il vraiment investir dans l'optimisation de la vitesse pour contrer le spam ?
  24. Pourquoi Google refuse-t-il de dévoiler le poids exact de ses facteurs de ranking ?
  25. Pourquoi Google utilise-t-il la vitesse comme facteur de classement ?
📅
Official statement from (4 years ago)
TL;DR

Google asserts that a single isolated metric like LCP does not reflect the true user experience. Interactivity and visual stability must be measured simultaneously to avoid phantom clicks and interface shifts. In practice, this necessitates optimizing INP and CLS alongside LCP, with occasionally conflicting trade-offs between these three pillars.

What you need to understand

What is the reasoning behind this multi-metric requirement? <\/h3>

Google is not trying to complicate the lives of SEO practitioners for its own sake. The real user experience is never summarized by just one number <\/strong> — a site can display its main content in 1.8 seconds (excellent LCP) while remaining completely frozen for 800 ms after the click (catastrophic INP).<\/p>

Splitt's statement reminds us of a fundamental truth: each metric captures a different aspect of UX <\/strong>. LCP measures the speed of displaying main content, INP (formerly FID) tracks responsiveness to interactions, and CLS quantifies visual stability. Ignoring any of these dimensions is like driving a car by only looking at one gauge — that of speed, while forgetting the fuel level and brake wear.<\/p>

How does Google combine these metrics into a ranking signal? <\/h3>

The exact mechanics remain opaque. Google talks about a "combined signal," but no public formula weighs LCP, INP, and CLS <\/strong> in the algorithm. What we know is: since 2021, Core Web Vitals form an inseparable set in assessing Page Experience.<\/p>

In practice, observations show that failing a single metric dramatically penalizes more than slightly improving all three <\/strong>. A CLS of 0.35 can drag down a site even with LCP and INP in the green. Google’s approach seems to resemble a minimum threshold for each metric rather than a weighted average — but again, everything is inference due to a lack of clear documentation.<\/p>

Why the emphasis on interactivity and stability now? <\/h3>

Modern JavaScript frameworks <\/strong> (React, Vue, Next.js) have multiplied cases of fast-loading sites that are slow to respond. The content appears quickly, but the main thread remains saturated: clicks don’t trigger anything for one or two seconds. Google reacted by replacing FID (too lenient) with INP in March 2024.<\/p>

For stability, the reason is simple: catastrophic CLS destroys trust <\/strong>. A button that jumps at the moment of clicking — due to a lazy-loaded ad banner — generates frustration and bounces. Google has observed a correlation between poor CLS and abandonment rates, hence its increasing weight in the overall signal.<\/p>

  • A single metric only captures one facet of UX <\/strong> — LCP, INP, and CLS measure three distinct issues <\/li>
  • Google combines these metrics into an opaque signal <\/strong> — no public formula, but a sudden failure in one dimension seems to penalize more than a mild improvement across all <\/li>
  • INP and CLS are gaining importance <\/strong> — React/Vue have multiplied quick yet frozen sites, and visual shifts correlate with user abandonment <\/li>
  • The approach seems to function on minimum thresholds <\/strong> — failing one metric weighs more heavily than averaging out elsewhere <\/li>

SEO Expert opinion

Does this statement align with what we observe in practice? <\/h3>

Yes, and it’s even a rare case where Google’s discourse matches real-world data <\/strong>. Audits regularly reveal sites with perfect LCP (< 2s) but disastrous INP (> 500 ms), especially on mobile. These sites see no visible gain in rankings despite a good LCP, validating the idea of a combined signal with multiple thresholds.<\/p>

However, Google remains strangely vague about the exact weighting <\/strong>. "Multiple metrics combined into one signal" tells us nothing about the relative weight of each dimension. Does a CLS capped at 0.1 compensate for a mediocre INP of 300 ms? Total mystery. [To be verified] <\/strong> — no public Google study quantifies this mechanic.<\/p>

What conflicting trade-offs does this approach create? <\/h3>

Let’s be honest: optimizing LCP, INP, and CLS simultaneously requires sometimes incompatible technical compromises <\/strong>. Loading fonts with preload improves LCP but may delay critical JS, degrading INP. Lazy-loading images below the fold optimizes LCP but risks triggering shifts (CLS) if ratios aren’t reserved.<\/p>

The worst-case scenario? E-commerce sites with dynamic carousels, Ajax filters, and ad blocks. Improving one metric often degrades another. There is no magic configuration that maximizes all three at once <\/strong> — it’s a balance to be found case by case, depending on business priorities and the technical constraints of the stack.<\/p>

In what cases does this multi-metric rule become secondary? <\/h3>

For purely informational sites with simple architecture — static blogs, lightweight showcase sites — LCP often remains the only real challenge <\/strong>. INP and CLS are naturally excellent there (no heavy JS, few layout shifts). Spending weeks scraping 10 ms off of INP when it’s already at 150 ms makes no strategic sense.<\/p>

Another edge case: SaaS within a login wall <\/strong>. Google only crawls public pages (landing, pricing, blog). If those pages are static and well-optimized, the Core Web Vitals of the app itself (dashboard, admin interface) do not impact SEO — even though the actual UX for logged-in users suffers. Here, the multi-metric obsession relates more to product UX than to SEO.<\/p>

Practical impact and recommendations

What should be measured concretely to comply with this approach? <\/h3>

Google Search Console and PageSpeed Insights <\/strong> provide the three CWV metrics with real-world data (CrUX). Always start by checking the P75 percentiles — this is the threshold Google uses to classify green/orange/red. A "good" site must score green on all three metrics simultaneously, not just on one.<\/p>

On the tools side, Lighthouse alone is no longer enough <\/strong>. It simulates in a lab but misses real cases of interactivity and shifts. Use WebPageTest with mobile 4G throttling to capture INP and CLS under conditions close to the real world. For complex sites, add RUM (Sentry, Datadog, New Relic) that tracks these metrics in production with real users.<\/p>

What technical errors cripple multiple metrics at once? <\/h3>

The capital sin: loading critical JS deferred or via monstrous bundles <\/strong>. This delays both LCP (if the content depends on JS to display) and explodes INP (thread saturated for seconds). Split the bundle, extract critical CSS inline, defer non-essential — classic but always neglected.<\/p>

The second trap: reserving space for images but forgetting iframes, ads, and embeds <\/strong>. A catastrophic CLS often comes from an ad banner without defined height, a Twitter widget pushing all content, or a lazy-loaded Google Map without a dimensioned container. Fix width/height or aspect-ratio on EVERY asynchronous element.<\/p>

How to prioritize optimizations when everything is red? <\/h3>

Start with the most degraded metric <\/strong>, the one blocking the overall "good" threshold. If your LCP is at 4s (bright red) but INP and CLS are correct, prioritize LCP: CDN, WebP/AVIF format, preload critical resources, aggressive lazy-loading below the fold.<\/p>

If all three metrics are mediocre, aim first for quick wins on CLS and INP <\/strong> — often easier to fix than LCP. Reserving visual spaces, deferring third-party scripts, reducing JS weight: these actions improve INP and CLS within days. LCP may require server overhaul, CDN migration, database optimization — which takes longer.<\/p>

  • Measure LCP, INP, CLS using CrUX (Search Console) and a RUM in production — Lighthouse alone is not enough <\/li>
  • Check the P75 percentiles — Google ranks according to this threshold, not the median <\/li>
  • Reserve width/height or aspect-ratio on images, iframes, ads, and embeds — avoids 80% of CLS <\/li>
  • Split JS bundles, extract critical CSS inline, defer non-essential — improves LCP and INP at once <\/li>
  • Prioritize the most degraded metric, then tackle quick wins on CLS/INP before addressing the complex LCP <\/li>
  • Test under real conditions (WebPageTest mobile 4G) — not just localhost on WiFi <\/li>
Simultaneously optimizing LCP, INP, and CLS requires a holistic view of the user journey and often delicate technical trade-offs. These tasks can become time-consuming, especially on complex stacks (React, WordPress with 20 plugins, e-commerce sites). If your team lacks resources or frontend expertise, hiring a performance-specialized SEO agency can drastically accelerate results — and avoid the well-meaning but misguided ideas that improve one metric while degrading the others.<\/div>

❓ Frequently Asked Questions

Peut-on scorer bon sur les Core Web Vitals avec un seul excellent LCP ?
Non. Google exige que LCP, INP et CLS passent tous trois le seuil « bon » (vert) pour considérer la page conforme. Un LCP parfait ne compense pas un INP ou CLS catastrophique.
L'INP a-t-il remplacé totalement le FID dans l'algorithme ?
Oui, depuis mars 2024, l'INP est la métrique officielle d'interactivité. Le FID n'est plus pris en compte dans le signal Page Experience ni dans les rapports Search Console.
Quelle métrique impacte le plus le classement SEO en cas de score médiocre ?
Impossible à affirmer avec certitude — Google ne publie aucune pondération. Les observations terrain suggèrent qu'un CLS très mauvais (> 0,25) pénalise plus visiblement qu'un INP moyen, mais cela varie selon secteur et requête.
Un site mobile-first doit-il optimiser les CWV desktop aussi ?
Google indexe et classe en mobile-first, donc les métriques mobile priment. Mais un desktop catastrophique dégrade l'UX réelle, et certains signaux comportementaux (rebond, temps sur page) peuvent indirectement affecter le ranking.
Les sites en JavaScript hydraté (Next.js, Nuxt) sont-ils désavantagés pour l'INP ?
Pas forcément. Bien configurés (streaming SSR, code-splitting fin, pas de gros hydration), ils peuvent scorer correctement. Mal configurés, ils saturent le thread principal et explosent l'INP — c'est une question d'implémentation, pas de framework.

🎥 From the same video 25

Other SEO insights extracted from this same Google Search Central video · published on 06/05/2021

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