<b>lastmod on the index file matters too</b>

<b>lastmod on the index file matters too</b>

The <code>&lt;lastmod&gt;</code> inside a sitemap index tells Google which child sitemaps changed — so it re-fetches only those. Most teams leave it static and lose the efficiency.

SOP:
Step 1 — Set each child's <code>&lt;lastmod&gt;</code> in the index to the newest lastmod among that child's URLs.
Step 2 — Update it only when a URL inside that child actually changes.
Step 3 — Leave unchanged children's lastmod untouched so Google skips re-fetching them.

Pass/fail:
— ✅ Changed children get a fresh index-level lastmod; unchanged ones don't.
— ❌ All children share today's date → Google re-fetches everything, every time.

Format: W3C datetime, e.g. <code>2026-06-13T14:22:00+00:00</code>.

Definition of done: index lastmod values move independently, only when their child's contents change.