The canonical tag indicates which page version Google should index, and it's always a best practice to include a canonical tag even if it's self referencing. We flag an invalid canonical when the page is missing the tag, or if you are referencing a non-indexable page. This should be fixed as soon as possible to ensure search engines know the focus page to index and serve in search results.

The right hand column of the report shows whether the canonical is "not set" (missing), "conflict" (e.g. it's referring to a non-indexable page) or invalid. After determining the cause of the problem, change or add the valid canonical tag yourself or by notifying your web developer. The canonical tag should always be located within in the head element of your page, and should never be injected with JavaScript. Learn more about this in our wiki and magazine.

If a page is canonicalized, it shouldn't receive any incoming organic sessions. A broken canonical can still result in the page being indexed and visited via search results. Use Google Analytics data to see which broken canonical receives the most traffic, and ensure you fix this first. Learn more in this article.