A sitemap index is a special XML file that lists other sitemap files instead of listing page URLs directly. It uses <sitemapindex> and <sitemap><loc> elements rather than <urlset> and <url><loc>. Large sites use it because a single sitemap is capped at 50,000 URLs / 50MB, so they split content into multiple child sitemaps and reference them all from one index.

You need one once you exceed 50,000 URLs or 50MB (uncompressed) in a single file. Even below that limit, a sitemap index is good practice for organizing content by type — separate sitemaps for pages, blog posts, products, and images — which lets you monitor indexation rate per section in Google Search Console.

It fetches your sitemap.xml and inspects the root XML element. A <sitemapindex> root with <sitemap><loc> children means it's an index pointing to other sitemaps. A <urlset> root with <url><loc> children means it's a regular sitemap of page URLs. This tool reports the type and, for an index, lists every child sitemap it references.

Submit just the sitemap index URL to Google Search Console. Google reads the index and automatically discovers and crawls every child sitemap listed inside it. You don't need to submit each child individually — though you can if you want per-sitemap reporting. Also reference the index in robots.txt with a Sitemap directive.

No. The sitemap protocol does not allow nesting indexes — a sitemap index can only reference regular sitemaps (urlset files), not other index files. If you have so many URLs that one index isn't enough, you'd submit multiple separate index files. This tool flags child entries that themselves appear to be indexes as a protocol violation.

It lists every child sitemap URL found in the index and reports the HTTP status of each (does it load with a 200, or is it a 404/redirect/error). A child sitemap that's listed but broken means a whole section of your URLs is invisible to search engines. It also surfaces the lastmod date when present.

Place it at a stable, crawlable URL — conventionally https://example.com/sitemap.xml or /sitemap_index.xml — and reference it in robots.txt with 'Sitemap: https://example.com/sitemap.xml'. Child sitemaps must be on the same host (or a verified host) as the index. Keep the URL consistent so search engines don't lose track of it.