Quick answer
lastmod helps search engines know when content changed.
Sitemap lastmod
lastmod helps search engines know when content changed. Missing lastmod is valid but optional.
Common causes
- No lastmod in url.
- Wrong date format.
How to fix
- Add lastmod in ISO 8601 (YYYY-MM-DD or full).
- Keep dates accurate.
FAQ
- lastmod required?
- No.
- Format?
- ISO 8601.
Fix it now
Try in validator (prefill this example)