What Google says
Google’s documentation on building a sitemap is direct: “Google ignores <priority> and <changefreq> values.” It does use <lastmod>, but only when the value is consistently and verifiably accurate, for example when it matches the page’s actual last modification. (Source: developers.google.com, Search Central, “Build and submit a sitemap”.)
So this analyzer isn’t about tuning. It shows what your sitemap says, flags values that break the protocol, and points you at the one date field that matters.
What we report
- changefreq distribution. How many URLs say always, hourly, daily, weekly, monthly, yearly or never, and any value outside that list (the protocol’s values are lowercase).
- priority distribution. Each value used, invalid ones (outside 0.0 to 1.0, or not a number), and the average priority per top-level section.
- Copy-paste defaults. When every URL has the same changefreq or priority, it’s a CMS default carrying no information.
- Claims vs lastmod. URLs that say “daily” or “weekly” but whose lastmod is months old. Either the page doesn’t change and the tag is noise, or it does and lastmod isn’t being updated.
- lastmod coverage. The share of URLs with a valid lastmod.
What to do instead
Put the effort into lastmod. Generate it from each page’s real content-change date, not the deploy time; leave it out rather than guess. Then keep the sitemap limited to canonical, indexable URLs. The sitemap validator checks the format of every entry, and the sitemap checker flags lastmod values that are all identical or in the future.