# What is Sitemap index? > A sitemap index is an XML file that lists other sitemap files, letting large sites split their URLs across several sitemaps and submit them as one. URL: https://yes-seo.com/glossary/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](https://yes-seo.com/glossary/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 ``` https://example.com/sitemaps/products-1.xml.gz 2026-10-28 https://example.com/sitemaps/blog.xml ``` Note the different root element — `sitemapindex` instead of `urlset` — and the `` entries in place of ``. 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](https://www.sitemaps.org/protocol.html#index)). - 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](https://developers.google.com/search/docs/crawling-indexing/sitemaps/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. - `` 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](https://yes-seo.com/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](https://yes-seo.com/glossary/crawl-budget) problems on large sites much easier to spot. ## Frequently asked questions ### Does the file have to be called sitemap_index.xml? No. Any name works as long as you reference it in robots.txt or submit it in Search Console. Popular SEO plugins use sitemap_index.xml, while WordPress core uses wp-sitemap.xml. ### Can a sitemap index list another sitemap index? No. Nesting isn’t supported: an index may only list regular sitemap files. If you need more structure, create several indexes and submit each one. ### Do small sites need a sitemap index? Not for size reasons. Under 50,000 URLs one sitemap is enough, but splitting by section can still make Search Console reports easier to read.