A URL that returns 200 OK but has content saying "page not found" or "this page no longer exists" is a soft-404. Google still crawls and partially indexes them, wasting crawl budget. This tool scans your sitemap sample and flags every soft-404 candidate.
Read the story behind this tool: Why I built this - silent crawl-budget killers.
Related: 404 Page Quality Audit / Sitemap lastmod truthfulness