Bing has reminded site owners that precise lastmod timestamps in XML sitemaps are critical for its AI driven crawler. Bing says the field is now a leading signal that determines which pages are recrawled and how often they appear in search results.
Key details on lastmod tags for AI indexing
- Use full ISO 8601 date and time, for example
2004-10-01T18:23:17+00:00. - Do not update
lastmodwhen the page itself has not changed. - Bing ignores the
changefreqandpriorityfields. - Submit sitemaps via
robots.txtor Bing Webmaster Tools. - Bing fetches a new sitemap immediately and rechecks it daily.
- A single sitemap can list up to 50,000 URLs. One index file can reference 50,000 sitemaps, allowing 2.5 billion URLs. Multiple index files scale capacity to 2.5 trillion URLs.
Background: crawl signals and IndexNow
Engineers Fabrice Canel and Krishna Madhavan explained that accurate lastmod data lets Bing skip unchanged pages and focus resources on fresh content. Combining XML sitemaps with the IndexNow protocol further improves coverage by sending real-time pings whenever a URL is added, updated, or removed. The dual approach is designed to keep inventories, news, and other time sensitive pages visible in AI powered search results.
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