About the Sitemap Checker
The Sitemap Checker auto-discovers a site's XML sitemap (root locations plus robots.txt declarations), validates the XML, distinguishes sitemap indexes from URL sets, follows child sitemaps, counts URLs and reports lastmod coverage — with warnings for the 50,000-URL and 50 MB limits.
Handy after a relaunch: confirm the sitemap only lists final, canonical URLs, then run a sample through the HTTP Status Checker — every sitemap URL should answer 200, never 3xx or 404.
The convention is /sitemap.xml in the domain root, and it should also be declared with a Sitemap: line in robots.txt — that is how search engines auto-discover it. This checker tries both locations automatically when you enter just a domain.
A single sitemap file may contain at most 50,000 URLs and must stay under 50 MB uncompressed. Larger sites split URLs across multiple files referenced by a sitemap index — this tool follows those indexes automatically.
Yes — Google has confirmed it uses lastmod as a crawl signal when it is accurate. Fake or always-current lastmod values get ignored. Missing lastmod is not an error, but accurate dates help fresh content get recrawled faster.