Noindex is a directive that instructs search engines to exclude a page from their search index. When a search engine crawler encounters a noindex directive, it processes the page but does not add it to the index, meaning the page will not appear in search results. The directive can be implemented via a meta tag in HTML or an X-Robots-Tag HTTP header.
The noindex directive is useful for pages that should be accessible to users but not discoverable through search engines. Common use cases include thank-you pages after form submissions, internal search results pages, paginated archive pages, staging or preview environments, and administrative dashboards. Technical SEO books on Amazon cover implementation strategies.
For URL shortening services, noindex is applied to splash pages, preview pages, and password-protected link pages. These pages serve a functional purpose for users but should not appear in search results, as they would provide a poor search experience.
An important nuance is that noindex does not prevent crawling. Search engines still fetch and process noindexed pages; they simply do not add them to the index. To prevent crawling entirely, robots.txt Disallow directives should be used. However, if a page is blocked by robots.txt, the search engine cannot see the noindex tag, which may lead to the page being indexed based on external signals. Web development SEO books on Amazon discuss these interactions.