What a valid sitemap needs
A urlset (or sitemapindex) root element in the namespace http://www.sitemaps.org/schemas/sitemap/0.9, a url element per page with an absolute loc, and optional lastmod dates in W3C format (2026-10-25 or 2026-10-25T10:00:00+00:00). Ampersands in URLs must be escaped as &.
changefreq and priority are allowed but ignored by Google. A lastmod in the future, or the same date on every URL, is a sign the dates are not real.
Questions
Why does an ampersand break my sitemap?
XML requires & to be written as &. A bare & makes the file invalid.
Does lastmod need a time?
No. A date like 2026-10-25 is valid; a time needs a time zone.
What is the limit for one sitemap?
50,000 URLs and 50 MB uncompressed. Larger sites split into several files listed in a sitemap index.
Is my data stored?
No. Sitemaps are read or built for the result you see and not kept.