Sitemap lastmod and dateModified: when to change them, and when not to.
Setting every page's lastmod to today feels harmless. It teaches Google to ignore the field. Here is the rule we use, and the code that enforces it on this site.
lastmod is one of the few signals you control directly about freshness. Most sites waste it.
What Google says
Google's sitemap documentation says it uses the lastmod value if it is consistently and verifiably accurate, for example by comparing it with the page's last modification. The value should reflect the last significant update: changes to the main content, the structured data or links are generally significant; a copyright date change is not. Google ignores priority and changefreq.
Change it, or don't
| Change | Update lastmod? |
|---|---|
| New section, rewritten paragraphs, new data | Yes |
| Corrected a figure or a fact | Yes |
| Changed structured data (author, FAQ, product details) | Yes |
| Added or changed meaningful internal links | Yes |
| Fixed a typo | No |
| Changed the footer, copyright year or site-wide CSS | No |
| Redeployed with no content change | No |
Keep the dates consistent
Three dates can describe a page: sitemap lastmod, schema.org dateModified, and a visible "updated" date. If they disagree, none of them looks verifiable. On this site all three come from the same field.
// services/siteUrls.js (sitemap)
INSIGHTS.forEach(e => urls.push({
loc: `${SITE_URL}/insights/${e.slug}`,
lastmod: e.updatedAt || e.date
}));
// partials/schema.ejs (Article schema)
'dateModified': piece.updatedAt || piece.date || '2026-05-01'An article gets an updatedAt only when its content changes meaningfully. When we corrected two figures in How AI engines choose sources, it got one; when we fix a typo, it doesn't. Static pages keep a hand-set lastmod in a list, with a comment saying never to derive it from "today".
Bing and IndexNow
Bing also reads lastmod. For faster pickup, pair an accurate sitemap with IndexNow, and ping only URLs whose content actually changed.
Checklist
- lastmod stored with the content, never computed at build or request time.
- Updated only for significant changes.
- Schema dateModified uses the same value.
- No priority or changefreq clutter.
- Sitemap submitted to Google Search Console and Bing Webmaster Tools; see our Bing checklist.
Questions people ask
Does Google use sitemap lastmod?
Yes, if it is consistently and verifiably accurate. Google compares it with the page's actual changes and ignores it on sites where it isn't reliable.
When should I update lastmod?
When the main content, structured data or links change significantly. Not for typo fixes, copyright years or site-wide template changes.
Should lastmod match dateModified in schema?
Yes. Generate both from the same stored value so the sitemap, structured data and any visible date agree.
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