What we check
Enter a domain and we find the sitemap through robots.txt (or /sitemap.xml), follow any sitemap index into its child files, and check every URL entry. Each file and each URL is read once, even when robots.txt lists both an index and the files inside it.
Per file
- It returns HTTP 200 with XML (not an HTML error page).
- The root element carries the
http://www.sitemaps.org/schemas/sitemap/0.9namespace. - At most 50,000 URLs and 50 MB uncompressed, the protocol’s limits. gzip files are decompressed first.
- It isn’t empty, and an index isn’t nested inside another index.
Per URL entry
<loc>is an absolute http(s) URL, under 2,048 characters, with&escaped as&, no spaces and no#fragment.- It’s on the same host as the sitemap. A www/non-www mix is flagged separately, because it usually means the sitemap lists URLs that redirect.
<lastmod>uses W3C Datetime (2026-09-23or a full timestamp with a time zone), is a real date and isn’t in the future.<changefreq>is one of always, hourly, daily, weekly, monthly, yearly or never, and<priority>is a number from 0.0 to 1.0.- No URL is listed twice, in the same file or across files.
Limits of one check
We read up to 20 sitemap files and 50,000 unique URLs within 25 seconds. On bigger sites, the result says how many files were left, and you can validate a child sitemap directly by entering its URL. For an overview of discovery, lastmod and host mix, start with the sitemap checker; for changefreq and priority, the frequency analyzer.