What is Sitemap index?

A sitemap index is an XML file whose only job is to point at other sitemaps. Instead of one giant list of URLs, you publish several smaller sitemaps — by section, content type or date — and one index that ties them together. Search engines fetch the index, then each child sitemap it lists.

Why use one

A single XML sitemap is capped at 50,000 URLs and 50 MB uncompressed, so beyond that, splitting is mandatory. Smaller sites benefit too:

• Better diagnostics — Search Console reports submitted and indexed counts per sitemap, so products.xml versus blog.xml shows which section has the indexing problem.
• Cheaper regeneration — only the file for the changed section needs rebuilding.
• One submission — submit the index once, and child sitemaps added later are picked up from it.

Example

<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <sitemap>
    <loc>https://example.com/sitemaps/products-1.xml.gz</loc>
    <lastmod>2026-10-28</lastmod>
  </sitemap>
  <sitemap>
    <loc>https://example.com/sitemaps/blog.xml</loc>
  </sitemap>
</sitemapindex>

Note the different root element — sitemapindex instead of urlset — and the <sitemap> entries in place of <url>. Child files may be gzip-compressed; the 50 MB limit applies to the uncompressed size.

Ways to split child sitemaps

• By content type — products, categories, articles, videos. The most useful split for diagnosing indexing problems.
• By date — one file per month for news or large archives, so old files rarely change and new URLs are easy to find.
• By numbered chunks — products-1.xml, products-2.xml — when a single type exceeds 50,000 URLs.

Rules worth knowing

• One index can list up to 50,000 sitemaps and must itself stay under 50 MB (sitemaps.org).
• No nesting: an index lists sitemaps, not other sitemap indexes.
• Child sitemaps should sit on the same site as the index. Search Console accepts up to 500 sitemap index files per site (Google’s guide to large sitemaps).
• The lastmod of each entry should say when that child file last changed, not when the index was rebuilt.

Common mistakes

• A child sitemap that starts returning 404 after a plugin change, so a whole section silently drops out of your inventory.
• <url> entries mixed into the index file — it may contain sitemap references only.
• Child sitemaps hosted on a CDN or other domain without cross-site verification.
• Submitting the index and every child separately, then losing track of which report is the real one.

Check it

Point the sitemap validator at your site: it detects a sitemap index, validates the XML and limits, and samples listed URLs for errors, redirects and noindex. Well-organized sitemaps also make crawl budget problems on large sites much easier to spot.

Frequently asked questions