Most sitemap generators emit priority=0.5 and changefreq=weekly for every URL because the CMS doesn't know better. Google ignores these signals when they're obviously meaningless. This audit grades whether your sitemap signals are believable — and flags lastmod values that don't match the actual page.
Read the story behind this tool: When Google ignores your sitemap signals →
The audit fetches the sitemap, parses up to 200 URLs, and spot-checks lastmod truthfulness on 10 random URLs.