sitemap entries include <lastmod>

<lastmod> lets agents do incremental re-ingestion — they can skip pages whose lastmod hasn't changed since their last crawl. Without it, agents either re-fetch everything every time (wasteful) or never update their snapshot (stale).

site Discoverability impl 1.0.0 sitemap-xml.has-lastmod

How the check decides

After parsing the sitemap, the check inspects every <url> entry and counts how many are missing a <lastmod> child. Passes if all entries have one. Fails with a count if any are missing. Warns if the sitemap has zero entries. Returns N/A if the sitemap couldn’t be parsed at all.

How to implement it

Most sitemap generators emit <lastmod> automatically from the source file mtime or the content’s last_updated frontmatter. If yours doesn’t, populate it from the most recent commit touching each page.

Pass

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <url>
    <loc>https://example.com/docs/install</loc>
    <lastmod>2026-04-01</lastmod>
  </url>
</urlset>

Fail

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <url>
    <loc>https://example.com/docs/install</loc>
  </url>
</urlset>