G14 — Chapter 7 - Technical SEO

Criterion G14 : Lazy loading images — guide + checklist

PART 1 - Fundamentals Chapter 7 - Technical SEO Keyword : lazy loading images

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

The **G14 — Lazy loading images** 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.

**G14 — Lazy loading images** (Chapter 7 - Technical SEO): loading=lazy for images outside viewport, do not lazy-load LCP element

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 rankings.

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: browser-side check (render + code). Recommended tool: **curl (headers)**.

  1. Open the page in Chrome → DevTools → Performance/Network tab.
  2. Run PageSpeed Insights 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: make a “clean” fix (no patch), then measure.

  • 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**: category page for aesthetic clinic in Lille
  • **Before**: Lighthouse: 34/100 (heavy JS, unoptimized images).
  • **After**: Lighthouse: 94/100 (lazy-load, compression, cache).
  • **Note**: Goal: stabilize LCP.

Checklist to tick

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

Frequently asked questions — G14

What is the most common mistake on “Lazy loading images”?

Applying an overly generic automatic pattern (same logic on all pages) without adding a differentiating element.

What is the fastest tool to check at scale?

For this type of criterion, a crawl (e.g. Screaming Frog) + targeted verification in curl (headers) 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?

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