- Class
- C2 Recommended
- Weight
- 4
- Severity on fail
- major
- Applies to
- Bing
Test this rule on a live site with the XML sitemap checker. Free, no account needed.
Scope and evidence
Evaluated on each sitemap file with lastmod values. The book marks this requirement DOCUMENTED RECOMMENDATION, SEARCH-ENGINE-SPECIFIC.
Fail conditions
Each condition has a stable code and a reason template. The evaluator fills the placeholders from observed values only; no sentence in a report is generated.
date_only_lastmod{n} lastmod values in {sitemap} contain a date but no time. Bing recommends ISO 8601 lastmod values including both the date and time.
The documented fix
Include the time and time zone in every lastmod value.
Sources, quoted
These are the passages the rule rests on, stored once in the knowledge base and emitted exactly as written. A citation marked for specific conditions appears only on findings with those codes.
“use standard ISO 8601 date formatting for lastmod values, including both the date and time”
[B-SITEMAP-2025] Keeping Content Discoverable with Sitemaps in AI Powered Search · Why lastmod Still Matters for AI Powered Indexing · last updated posted 2025-07-31
https://blogs.bing.com/webmaster/2025/7/Keeping-Content-Discoverable-with-Sitemaps-in-AI-Powered-Search/