Definition
What this term means
An HTTP response header that communicates the exact date and time a web page was last updated. When a crawler or AI system requests a page, the Last-Modified header tells it how recent the content is. This header works alongside other freshness signals to help AI systems assess whether content is current and relevant, or potentially outdated.
Why it matters
The business impact
AI systems prefer fresh, well-maintained content, especially for topics where information changes frequently. Accurate Last-Modified headers reinforce freshness signals, making your content more likely to be selected over older competing sources. Conversely, stale or missing Last-Modified headers can cause AI systems to deprioritise your content in favour of more recently updated alternatives.
Used in context
How you might use this term
“A company was losing AI citations to competitors whose content was objectively less comprehensive but more recently updated. After implementing accurate Last-Modified headers and establishing a regular content refresh schedule, their citation rate recovered as AI systems recognised their content as both authoritative and current.”