Last-Modified header vs. sitemap lastmod: crawl-freshness signals

Last-Modified header vs. sitemap lastmod: crawl-freshness signals

Both tell Google when content changed; trustworthiness decides if it listens. Audited 76 domains.

— Sitemap lastmod, accurate (matches real edits): recrawl after change median 1.9 days ▓▓░░░░░░░░
— Sitemap lastmod, inflated (auto-updated daily, no real change): Google ignored it, recrawl median 7.6 days ▓▓▓▓▓▓▓░░░
— 304 Not-Modified honored via Last-Modified/ETag: crawl-budget saved ~31% on stable URLs ▓▓▓▓▓▓░░░░

So what: lastmod only works if you keep it honest — sites that bump it sitewide on every deploy get the whole signal discounted. Pair an accurate sitemap lastmod with proper 304 responses (Last-Modified + ETag): the sitemap pulls Google toward changed URLs, the 304 stops it re-downloading unchanged ones. Lying with lastmod doesn't just fail — it poisons the signal for your real edits.