Why it matters to a buyer
Noindex is a deliberate, page-level control that is genuinely useful for keeping thin pages, internal search results, or duplicate filtered pages out of search, and it is also one of the most common accidental causes of a site losing all its traffic: a noindex tag left on from a staging environment, or applied site-wide by a CMS setting, will silently drop the whole site from search with no warning. A buyer should have noindex usage checked specifically after any launch, migration or redesign.
How it is measured or applied
Google requires the noindex directive to be visible to the crawler, meaning the page must not also be blocked in robots.txt, since a blocked page can never be crawled to discover the noindex tag in the first place. It is applied selectively to low-value pages, like internal search results or thin tag archives, rather than broadly. It is checked with Search Console's URL inspection tool, which shows whether Google actually saw a noindex directive on a given URL, and with a site-wide crawl after any deployment to catch a noindex tag applied more broadly than intended.
Sources
- Block Search indexing with noindex, Google Search Central
