sitemap index
Also called: sitemap index file, index sitemap, sitemap index xml
A sitemap index is an XML file that lists the URLs of multiple child sitemaps. It lets a large site stay within the per-sitemap cap of 50,000 URLs (or 50MB uncompressed): you submit the one index file, and search engines discover every sitemap it references.
Think of a sitemap index as a table of contents for your sitemaps. Search engines cap a single sitemap at 50,000 URLs or 50MB uncompressed, so a large store or publisher splits its URLs across several sitemaps (say, one per section) and lists them all in one index file.
Structure and rules
The index uses <sitemapindex> as the root, with one <sitemap> block per child. Each block needs a <loc> (the child sitemap’s URL) and can carry an optional <lastmod>:
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<sitemap>
<loc>https://example.com/sitemap-products.xml</loc>
<lastmod>2026-07-01</lastmod>
</sitemap>
</sitemapindex>A few constraints matter. One index can reference up to 50,000 sitemaps and must stay under 50MB. The child sitemaps have to sit on the same site as the index, in the same directory or lower in the hierarchy. An index points at regular sitemaps, not at other index files. You submit the single index URL in Search Console (Google accepts up to 500 sitemap index files per site) and reference it in robots.txt with a Sitemap: line. Crawlers then walk every sitemap the index names, so you maintain one entry point instead of registering each file by hand.
How it affects your traffic
For big sites, an index is how new and updated URLs actually get discovered and recrawled quickly. Segmenting child sitemaps by section (posts, products, categories) also lets you read the indexed-versus-submitted count per sitemap in Search Console, so you can see exactly which part of the site Google is skipping instead of guessing. When a section quietly grows past the 50,000-URL cap, the overflow URLs drop out of the sitemap and stop getting crawled. Setting up and segmenting sitemaps correctly is part of our Technical SEO work.
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