Definition

A sitemap index file is an XML file that references multiple individual sitemaps, allowing a site to group and submit them together — used when a single sitemap would exceed the size limits.

Google limits an individual sitemap to 50,000 URLs and 50MB uncompressed; larger sites split their URLs across several sitemaps and list those files in a sitemap index. A single index can reference up to 50,000 sitemaps, and the index itself is what gets submitted in Search Console or referenced from robots.txt. Every sitemap referenced must still comply with the standard sitemap size limits.

Examples

• Large catalogue

  A marketplace with 400,000 product URLs splits them into ten sitemaps of 40,000 URLs each and lists all ten in a single sitemap index submitted to Search Console.

• Referencing from robots.txt

  A site points to its sitemap index with a `Sitemap:` line in robots.txt, so crawlers discover every child sitemap from one entry.

Sources

• Google Search Central — Manage your sitemaps with a sitemap index file

Related terms

• Sitemap
  A file, usually XML, that lists URLs on a site so search engines can discover and crawl them more efficiently.
• Crawl Budget
  The number of URLs a search engine crawler will fetch and the rate at which it fetches them on a given site.
• robots.txt
  A plain-text file at the root of a domain that tells crawlers which paths they may or may not request.

Where QueryCatch uses this

• Sitemap Optimisation
• SEO Audit