The `rel=”canonical”` tag is a powerful signal that tells search engines which version of a page to index. However, this signal becomes a critical error when it points to a non-indexable URL. This creates a conflicting and nonsensical instruction: “This page is a duplicate of another page, but the other page shouldn’t be in the index either.” Faced with this contradiction, search engines will often ignore the canonical tag and may even de-index the original page, making your content invisible in search results.
Think of it as forwarding your mail to a vacant, demolished building. The instruction to forward the mail is clear, but the destination is invalid. The result is that your mail gets lost. Similarly, canonicalizing to a non-indexable URL is a wasted signal that can cause your page’s SEO value to vanish. For a broader look at canonicalization, see our main guide on canonical issues.
Why a Canonical URL Must Be Indexable
The entire purpose of a canonical tag is to point to the single, authoritative, *indexable* version of a page. As Google’s documentation makes clear, the canonical URL you select must be a valid, live page.
- It’s a De-indexing Signal: Pointing to a page that is noindexed, blocked by robots.txt, or returns a 404 error can cause the original page to be dropped from the index.
- It Wastes Crawl Budget: You are forcing search engines to crawl two URLs, only to find that neither is a valid indexing candidate.
A Step-by-Step Guide to Fixing the Conflict
The goal is to ensure that every `rel=”canonical”` tag on your site points to a live, indexable, 200 OK page. For more on this, check out this guide to canonicalization from Ahrefs.
Example: Fixing a Non-Indexable Canonical
<!-- Before: Canonical points to a noindexed page --> <link rel="canonical" href="https://example.com/noindexed-page" /> <!-- After: Canonical points to an indexable page --> <link rel="canonical" href="https://example.com/indexable-page" />For more on this topic, see our guide on on-page SEO.
Frequently Asked Questions
What makes a canonical URL ‘non-indexable’?
A canonical URL is considered non-indexable if it has a `noindex` tag, is blocked by robots.txt, returns a 404 or 5xx status code, or redirects to yet another page. All of these signals prevent it from being a valid, indexable target for a canonical tag.
Does this apply to other link tags?
Yes. Any link tag that is meant to signal a relationship between pages, such as `rel=”alternate” hreflang` or `rel=”amphtml”`, should also point to an indexable, canonical URL.
How can I find all the pages that point to a non-indexable canonical?
The most effective way is to use a website crawler like Creeper. It will scan every page, extract the canonical URL, and then crawl that URL to check its indexability status, flagging any instances where the canonical target is blocked, broken, or noindexed.
Are your canonical signals being wasted? Start your Creeper audit today to find and fix these critical errors.