There are several technical issues that can hinder a URL from being indexed by search engines like Google or Bing:
- URL blocked by robots.txt: If the page is blocked by the website’s robots.txt file, search engines will not be able to crawl and index it.
- Meta Robots is noindex: The “noindex” meta tag in the page’s HTML code can instruct search engines not to index the page.
- Canonicalization issues: If there are multiple versions of the same page (e.g. with different URLs), search engines might have trouble deciding which one to index. Or your canonical simply points towards a wrong URL.
- Crawl errors: If the page returns a 4XX error (URL not accessible) or is otherwise not accessible (e.g. 5XX server error), search engines may not be able to crawl and index it.
- Low-quality or thin content: If the page has low-quality or thin content, search engines may not consider it important enough to index.
- Lack of internal and external links: If the page has no links pointing to it (internal or external), it can be difficult for search engines to discover and index it. (very rare)
- Duplicate content: If the page’s content is identical or very similar to other pages on the web, search engines may not index it to avoid displaying duplicate results.
Let’s do a short excursion into the duplicate content issue:
- Google partially also refuses to index pages if already meta-title and meta-description are looking identical
Search engines like Google use the page title and description as a key part of their evaluation of a page’s relevance and quality, and having duplicate or very similar titles and descriptions can be seen as a sign of low-quality or spammy content. As a result, having identical or near-identical titles and descriptions across multiple pages, with only slight variations in keywords, can negatively impact the ability of these pages to be indexed and rank well in search results.
It’s important to write unique and descriptive page titles and descriptions that accurately reflect the content of the page, and to avoid using overly repetitive or spammy tactics.
This is a special challenge e.g. for optimizing category trees of e-commerce shops that should contain Category Name + Discount + CTA wording.