Official statement
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- □ Le rendu JavaScript de Google est-il vraiment devenu fiable pour l'indexation ?
- □ Google collecte-t-il réellement tous vos logs JavaScript pour le SEO ?
- □ Les infos de layout CSS sont-elles vraiment inutiles pour le SEO ?
- □ Faut-il vraiment bloquer les CSS dans le robots.txt pour accélérer le crawl ?
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- □ Pourquoi la structure de liens mobile-desktop peut-elle saboter votre indexation mobile-first ?
- □ Google privilégie-t-il certains services de prerendering pour le crawl ?
- □ Faut-il encore utiliser le cache Google pour vérifier le rendu JavaScript ?
- □ Les outils Search Console suffisent-ils vraiment pour auditer le rendu JavaScript de vos pages ?
- □ Google rend-il vraiment CHAQUE page avec JavaScript avant de l'indexer ?
- □ Le tree shaking JavaScript est-il vraiment indispensable pour le SEO ?
- □ Chrome stable pour le rendu Google : quelles conséquences réelles pour votre SEO technique ?
- □ HTTP/2 pour le crawl : faut-il abandonner le domain sharding ?
Google officially recommends delaying the loading of trackers and analytics solutions as much as possible to avoid slowing down the primary user experience. Specifically, only the critical code needed to display content above the fold should be inline or loaded first. This directive is aimed directly at improving Core Web Vitals, particularly LCP and FID, which now impact search rankings.
What you need to understand
Why does Google emphasize delayed loading of trackers? <\/h3>
Splitt's statement aligns with a clear rationale: third-party scripts — analytics, advertising trackers, conversion pixels — are often the main culprits of performance issues. These external resources add loading time, block rendering, and consume bandwidth without directly contributing to the display of content visible to the user.<\/p>
Google is now measuring actual user experience through Core Web Vitals (CWV), collected from Chrome over millions of sessions. An analytics script that runs at the start of loading can delay First Input Delay or degrade Cumulative Layout Shift. By deferring these scripts, critical resources are freed up to display the main content faster<\/strong>.<\/p> The necessary code is that which allows displaying content above the fold<\/strong>: structural HTML, critical CSS for initial rendering, essential fonts, hero images. Everything else — analytics, chatbots, social sharing buttons, lazy loading of secondary images — can be deferred.<\/p> In practical terms, if your Google Analytics blocks rendering for 300 ms because it is loaded in a <head> synchronous<\/strong> manner, you are sacrificing performance for a data point that could very well be collected 2 seconds later. The user does not see the difference in their analytics, but they see — and feel — the delay in page display.<\/p> Googlebot executes JavaScript, but it has a limited crawl and rendering budget<\/strong>. The heavier your page is on third-party scripts, the more it consumes resources on Google's side to be analyzed. By delaying trackers, you reduce the initial DOM load and speed up rendering time for the bot.<\/p> Moreover, a fast site generates positive engagement signals<\/strong>: lower bounce rates, higher time spent on the page, better conversion rates. These indirect metrics influence ranking, even if Google does not directly use them as a ranking factor. A site that loads quickly is a site that performs better, period.<\/p>What exactly do we mean by 'absolutely necessary code'? <\/h3>
How does this directive impact crawling and indexing? <\/h3>
defer<\/code>, async<\/code>, or loading via JavaScript after DOMContentLoaded<\/code><\/li>
SEO Expert opinion
Is this recommendation really new or just a reminder? <\/h3>
Let's be honest: deferring third-party scripts<\/strong> has been a web performance best practice since at least 2010. What changes is that Google is now making it an explicit SEO directive related to Core Web Vitals. Previously, it was an optional optimization; now, it’s a direct ranking lever.<\/p> The nuance is that many sites still load Google Analytics, Tag Manager, Facebook Pixel, and a dozen other scripts in blocking mode<\/strong>, out of laziness or lack of understanding. Splitt is hitting where it hurts — and it’s justified. I have seen sites lose 15-20 Lighthouse score points solely due to poorly loaded analytics scripts.<\/p> The main friction point is precise audience measurement<\/strong>. If you defer your tracker too much, you run the risk of missing ultra-short sessions (users who bounce in less than a second). Some analytics tools rely on early events to measure the complete journey — delaying their loading can create gaps in the data.<\/p> Another edge case: dynamically personalized scripts<\/strong> (A/B testing, personalized content) that need to execute before rendering to avoid a ‘flash’ of non-targeted content. Here, you have to balance performance and functionality. [To be verified]<\/strong>: Google does not specify how to handle these situations where the tracker directly impacts user experience.<\/p> Absolutely. Sites that have migrated their trackers to defer/async<\/strong> or via post-load tag managers have consistently improved their CWV. I measured gains of 30-40% on LCP just by moving Google Analytics after However, be careful: some poorly coded analytics tools do not support delayed loading well and may generate JavaScript errors if the DOM is not fully ready. You need to test in real conditions<\/strong>, especially on 3G mobile, to ensure that the deferred loading doesn’t break anything. A script that fails in async mode can be worse than a slow script in synchronous mode.<\/p>In what situations can this rule be problematic? <\/h3>
Do real-world observations confirm this directive? <\/h3>
window.onload<\/code>.<\/p>
Practical impact and recommendations
What actionable steps should be taken to apply this directive? <\/h3>
First step: audit all third-party scripts<\/strong> present on your pages. Use Chrome DevTools → Coverage to identify resources that block rendering. Anything that is not used in the early moments should be a candidate for deferral.<\/p> Next, implement asynchronous loading via Classic error: moving a script to Another trap: assuming that all trackers support deferral. Some legacy or poorly designed tools expect to be loaded synchronously<\/strong> and fail in async mode. Always test in a staging environment before pushing to production. And keep an eye on your analytics dashboards for a few days after deployment to catch any data collection anomalies.<\/p> Run a Lighthouse audit (PageSpeed Insights) and look at the section “Eliminate render-blocking resources”<\/strong>. Any third-party script appearing here is a candidate for deferral. Also, check the waterfall in DevTools → Network: trackers should load after<\/strong> the main content, not in parallel or before.<\/p> To measure the real impact, compare your Core Web Vitals before/after via Search Console or CrUX Report. A gain of 0.5 seconds on LCP is considered significant. If you see no change after deferring your scripts, it means the bottleneck is elsewhere — likely on the server side or with unoptimized images.<\/p>async<\/code> or defer<\/code> for scripts that allow it. For more complex trackers (Tag Manager, Facebook pixels), consider a post-onload loading<\/strong> approach using a JavaScript event handler. Simple example: window.addEventListener('load', function() { /* load analytics here */ });<\/code>.<\/p>What mistakes should be avoided when deferring trackers? <\/h3>
async<\/code> without checking dependencies. If your Tag Manager loads other scripts that in turn call others, you risk race conditions<\/strong> — some events trigger before the tracker is ready, and you lose data.<\/p>How can I check if my site complies with this recommendation? <\/h3>
defer<\/code> or async<\/code>, or load them via JavaScript after window.onload<\/code><\/li>
❓ Frequently Asked Questions
Peut-on vraiment différer Google Analytics sans perdre de données de session ?
Quelle différence entre async et defer pour les trackers ?
Le chargement différé des trackers impacte-t-il le consentement RGPD ?
Les pixels de conversion publicitaire (Facebook, Google Ads) supportent-ils le chargement différé ?
Comment gérer les scripts qui dépendent les uns des autres en mode asynchrone ?
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