What is an XML sitemap?

Rules from Google

A single sitemap is limited to 50 MB uncompressed or 50,000 URLs; larger sites use several files listed in a sitemap index, and Google says you can optionally submit that single index file. URLs should be fully qualified. Google uses lastmod only when it is consistently and verifiably accurate, and it ignores priority and changefreq.

What belongs in it

Only canonical, indexable URLs that return 200: no redirects, no errors, no noindex pages and no duplicates. The sitemap can be declared in robots.txt with a Sitemap: line and submitted in Search Console and Bing Webmaster Tools.

An example

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <url><loc>https://example.com/guides/ssl</loc><lastmod>2026-10-20</lastmod></url>
</urlset>

The common error is a lastmod equal to the deploy date on every URL: it says everything changed today, and search engines learn to ignore the field. Set it to the date the page’s content really changed. The file must use the production host in every loc, and a staging host left in it sends crawlers to the wrong site.

A sitemap supplements links; it does not replace them. After a migration, fetch each URL it lists and check that none redirects, fails or carries noindex, because a sitemap full of such URLs wastes crawl attention and weakens trust in the file.

What to check

That the file is reachable, valid XML and on the production host, that a sample of its URLs return 200 and canonicalise to themselves and that lastmod reflects real changes.

Sources

Read on 26 October 2026. Standards and vendor pages change; confirm the current text before you rely on it.

• Google Search Central, Build and submit a sitemap (developers.google.com)