G3 — Chapter 7 - Technical SEO

Criterion G3 : Core Web Vitals - CLS — guide + checklist

PART 1 - Fundamentals Chapter 7 - Technical SEO Keyword : core web vitals - cls

This criterion seems “simple”, but it creates many discrepancies in production.

The **G3 — Core Web Vitals - CLS** criterion is part of our SEO checklist (335 criteria). Here, you have a **practical** method to check and fix it — with a concrete example.

What exactly this criterion covers

This criterion seems “simple”, but it creates many discrepancies in production.

**G3 — Core Web Vitals - CLS** (Chapter 7 - Technical SEO): Cumulative Layout Shift < 0.1, defined image/ad dimensions

Why it matters (SEO + UX)

Why it matters: it is a UX point that eventually translates into SEO. When poorly applied, we often observe: ambiguity (wrong associated query), duplication between pages, or performance loss on bounce rate.

On high-volume generated sites, this criterion also acts as a **safeguard**: a stable rule prevents 1,000 errors at once.

How to check (step by step)

Approach: tool-assisted test (validator / performance). Recommended tool: **PageSpeed Insights**.

  1. Open the page in Chrome → DevTools → Performance/Network tab.
  2. Run Lighthouse and note the main weak point.
  3. Check if the problem repeats on mass-generated pages.

Tip: first isolate 10 “representative” URLs (top pages + generated pages) before scaling the fix.

How to fix properly

Strategy: fix the minimum necessary, then stabilize.

  • Fix the biggest cost source (images, JS, fonts, cache).
  • Retest, then apply to the template (not page by page).
  • Add a safeguard: weight budget (KB) and CI check if possible.

Then: re-crawl 50–200 URLs, then monitor Search Console over 7–14 days (impressions/CTR/indexing).

Concrete example (illustrative)

Example (illustrative):

  • **Context**: service landing page for a restaurant in Marseille
  • **Before**: Lighthouse: 48/100 (heavy JS, unoptimized images).
  • **After**: Lighthouse: 86/100 (lazy-load, compression, cache).
  • **Note**: Goal: stabilize LCP.

Checklist to tick

  • [ ] Measure before/after
  • [ ] Respect: defined ads
  • [ ] Improvement on template
  • [ ] No CWV regression
  • [ ] Cache and compression OK
FAQ

Frequently asked questions — G3

What is the most common mistake on “Core Web Vitals - CLS”?

Trying to “optimize” by adding too many keywords, which degrades readability and creates repetitions.

What is the fastest tool to check at scale?

For this type of criterion, a crawl (e.g. Screaming Frog) + targeted verification in PageSpeed Insights is generally the fastest combo.

How to prevent this from happening on 10K generated pages?

Freeze an auto-generation rule (title/structure/schema/URLs) + add automatic control (crawl or test) before production import.

Ready to go from theory to action?

Validate this criterion with an audit, then deepen the method in the Academy.

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