G18 — Chapter 7 - Technical SEO

Criterion G18 : Mobile-first indexing — guide + checklist

PART 1 - Fundamentals Chapter 7 - Technical SEO Keyword : mobile-first indexing

Here we talk about a criterion that often makes a difference in audits.

The criterion **G18 — Mobile-first indexing** 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

Here we talk about a criterion that often makes a difference in audits.

**G18 — Mobile-first indexing** (Chapter 7 - Technical SEO): Verify that the mobile version = desktop (content, schema, meta)

Why it matters (SEO + UX)

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

On volume-generated sites, this criterion also serves 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: **WebPageTest**.

  1. Open the page in Chrome → DevTools → Performance/Network tab.
  2. Run WebPageTest 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: apply a rule, then check neighboring pages.

  • 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: recrawl 50–200 URLs, then monitor Search Console for 7–14 days (impressions/CTR/indexing).

Concrete example (illustrative)

Example (illustrative):

  • **Context**: product sheet for a law firm in Paris
  • **Before**: Lighthouse: 43/100 (heavy JS, unoptimized images).
  • **After**: Lighthouse: 96/100 (lazy-load, compression, cache).
  • **Note**: Goal: stabilize INP.

Checklist to tick

  • [ ] Measure before/after
  • [ ] Respects: meta
  • [ ] Improvement on template
  • [ ] No CWV regression
  • [ ] Cache and compression OK
FAQ

Frequently asked questions — G18

What is the most common mistake on “Mobile-first indexing”?

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

Which tool is the fastest for large-scale checking?

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