Sitemap Index
A sitemap index is an XML file that lists other sitemap files rather than individual pages. It lets large or complex websites split their URLs across several sitemaps while giving search engines a single file to find them all.
How a sitemap index works
A standard XML sitemap lists page URLs. A sitemap index sits one level above. It uses a <sitemapindex> root element, with a <sitemap> entry for each child file containing its <loc> and optionally a <lastmod> date.
You submit the index once, and search engines follow it to each child sitemap.
When you need one
- Size limits: a single sitemap can hold up to 50,000 URLs or 50MB uncompressed. Larger sites must split them.
- Organisation: separate sitemaps for products, categories, blog posts and locations make reporting easier.
- Different types: you can include an image sitemap, video or news sitemap alongside page sitemaps.
- CMS defaults: many platforms, including WordPress with common SEO plugins, create an index automatically even for small sites.
An index can list up to 50,000 sitemaps. Sitemap indexes cannot be nested, so an index should list sitemaps, not other index files.
How to create and submit one
- Group URLs into logical sitemaps, keeping each under the limits.
- Create the index file listing each sitemap’s full, absolute URL.
- Host the index and sitemaps on the same site they describe, usually at the root.
- Add a Sitemap line pointing to the index in your robots.txt file.
- Submit the index in Google Search Console and Bing Webmaster Tools.
- Check the reports for each child sitemap: discovered URLs, errors and indexing status.
Why splitting helps diagnosis
When sitemaps are grouped by page type, Search Console’s page indexing report can be filtered by sitemap. If product pages are being excluded but blog posts are fine, you can see it straight away. This makes it easier to spot problems like thin content in one section.
Example structure
A mid-sized online shop might use an index at /sitemap_index.xml that lists five child files: one for products, one for categories, one for blog posts, one for static pages such as delivery and returns, and an image sitemap. If the product catalogue grows past 50,000 URLs, it is split into product-sitemap-1.xml, product-sitemap-2.xml and so on, each listed in the same index.
Each child sitemap should only contain canonical, indexable URLs that return a 200 status. The lastmod date on each index entry should reflect when that child file last genuinely changed. Search engines use these dates as hints about what to recrawl, so accurate dates make the whole system more efficient, particularly for large sites with limited crawl budget.
Common mistakes
- Listing child sitemaps that return errors or redirects.
- Including non-canonical, redirected or noindexed URLs in the child sitemaps.
- Lastmod dates that update every day regardless of real changes, which teaches search engines to ignore them.
- Forgetting to remove old sitemaps after a restructure.
Further reading: Google on managing large sitemaps.
Key Takeaways
- A sitemap index is a file that lists other sitemap files.
- Each sitemap is limited to 50,000 URLs or 50MB uncompressed.
- Splitting sitemaps by page type makes indexing problems easier to spot.
- Submit the index in Search Console and reference it in robots.txt.
- Sitemap indexes cannot be nested inside other indexes.
Related Terms
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