What this checks
This fetches your sitemap and validates it against the requirements that actually matter to search engines:
whether the XML is well-formed, whether the root element is the expected <urlset> (or
<sitemapindex> for an index file), whether each listed URL is a valid absolute address, and
whether the file stays within Google's limits of 50,000 URLs and 50MB uncompressed per sitemap file.
Why both urlset and sitemapindex are treated as valid root elements
A sitemap index file doesn't list pages directly - it lists other sitemap files, which is exactly how larger
sites stay under the 50,000-URL-per-file limit without needing one impossibly large file. Recognizing
sitemapindex as a legitimate root element alongside urlset means this tool validates
both the direct and the indexed approach correctly, rather than flagging a properly structured index file as
malformed.
Why a structurally valid sitemap doesn't guarantee good indexing
Does a clean validation guarantee good indexing? No - a structurally valid sitemap is necessary but not sufficient. Search engines still decide independently which listed URLs to actually crawl and index based on many other factors, like content quality and site authority, that have nothing to do with the sitemap file's own structure.
Why each finding is shown with its own severity level instead of one single pass/fail result
An error (malformed XML), a warning (approaching the URL count limit), and pure information (file size) each call for a different response from you - showing each finding tagged by its actual severity lets you prioritize fixing what's broken first, rather than treating every issue the validator surfaces as equally urgent.