This tool is designed to verify the presence or absence of any sitemaps (XML) available on the given website. It analyzes the robots.txt file; if there is no sitemap section, it loads the file from the default location and returns everything found, including links to other sitemaps and pages from your website.
A sitemap.xml is a file where you provide information about the pages on your site. Search engines like Google read this file to crawl your site more efficiently. A sitemap tells search engines which pages you think are important in your site, and also provides valuable information.