1.7 XML sitemapsMediumVerified
lastmod wrong date format
lastmod has to be in the W3C datetime format. A non-conforming date is ignored, so the freshness hint I meant to give is silently dropped.
What it is
Non-W3C date format.
Why it matters
Invalid dates are ignored.
How to fix it
Use W3C/ISO 8601 dates.
How to find it on your site
- Check the lastmod format, it should look like 2026-06-13 or a full ISO timestamp.
- Validate the sitemap with a sitemap validator.
- Fix the generator to output W3C datetime format.
- Re-validate.
Cross-reference to ranking and citation factors
An invalid date is discarded, so the page loses its freshness hint. Correct formatting is a small but real crawl-efficiency win.
Impact
Low-medium. Direct.
Evidence
Use W3C datetime format for lastmod. Google Search Central, Build and submit a sitemap