GlossarySEO
What is a sitemap index file?
Also called: sitemap index file, sitemap_index.xml, multiple sitemaps
Definition
A sitemap index is an XML file that lists other sitemap files instead of pages. It lets large sites split URLs across several sitemaps and submit them all through one file.
Sitemap index, explained
A single sitemap has limits: Google's docs set it at 50,000 URLs or 50MB uncompressed. A sitemap index gets around that by listing sitemap files in <sitemap> entries, each with a <loc> and an optional <lastmod> for when that sitemap file changed. Google's large-sitemaps guide says an index can hold up to 50,000 loc entries, and you can submit up to 500 sitemap index files per site in Search Console.
There are structural rules. The index can only point to sitemaps, not to other index files, so no nesting. The listed sitemaps must be on the same site as the index, in the same directory or lower in the hierarchy, unless you've set up cross-site submission.
The real benefit for most startups isn't size, it's visibility. Splitting URLs by page type into separate sitemaps, such as core pages, blog, comparisons, glossary and programmatic families, means Search Console's Sitemaps and Page indexing reports can be filtered per sitemap. You can see that your blog is 95% indexed while a programmatic family sits at 30%, which tells you exactly where the quality problem is.
Reference the index from robots.txt with a Sitemap: line and submit it once in Search Console. Keep each child sitemap limited to canonical, indexable URLs with honest lastmod dates.
Why it matters for founders
When you're scaling pages, per-section indexing data is how you find the weak page family before it drags down the rest. A sitemap index is the easiest way to get it.
Example
Your /sitemap.xml is an index pointing to sitemap-pages.xml, sitemap-blog.xml and sitemap-compare.xml. In Search Console, you filter the Page indexing report by each and see comparisons lagging.
Common mistakes
- Nesting one index inside another.
- Pointing to sitemaps on a different host without cross-site setup.
- One giant sitemap that hides which section has problems.
- Updating every child sitemap's
lastmodon each deploy.
Sources
- Google Search Central: Manage your sitemaps with a sitemap index file
- Google Search Central: Build and submit a sitemap
Checked
Related terms
- XML sitemapAn XML sitemap is a file that lists the URLs you want search engines to crawl and index, optionally with the date each one last changed. It helps discovery; it doesn't guarantee indexing.
- lastmod
lastmodis the optional sitemap field that states when a URL's content last changed. Google uses it to schedule recrawls, but only if the dates are consistently accurate. - Page indexing reportThe Page indexing report in Search Console shows how many of your known URLs are indexed and groups the rest by the reason they aren't, like noindex, redirect, duplicate, 404 or crawled but not indexed.
- Programmatic SEOProgrammatic SEO is creating many search-targeted pages from structured data and templates, such as one page per integration, city or comparison. It works when each page answers a real query with unique, useful data.