Monday, April 08, 2013 at 3:09 PMWebmaster Level: Intermediate to Advanced Including a rel=canonical link in your webpage is a strong hint to search engines your about preferred version to index among duplicate pages on the web. It’s supported by several search engines, including Yahoo!, Bing, and Google. The rel=canonical link consolidates indexing properties from the duplicates, like their inbound links, as well as specifies which URL you’d like displayed in search results. However, rel=canonical can be a bit tricky because it’s not very obvious when there’s a misconfiguration.
While the webmaster sees the “red velvet” page on the left in their browser, search engines notice on the webmaster’s unintended “blue velvet” rel=canonical on the right.We recommend the following best practices for using rel=canonical:
- A large portion of the duplicate page’s content should be present on the canonical version.
- Double-check that your rel=canonical target exists (it’s not an error or “soft 404”)
- Verify the rel=canonical target doesn’t contain a noindex robots meta tag
- Make sure you’d prefer the rel=canonical URL to be displayed in search results (rather than the duplicate URL)
- Include the rel=canonical link in either the <head> of the page or the HTTP header
- Specify no more than one rel=canonical for a page. When more than one is specified, all rel=canonicals will be ignored.
One test is to imagine you don’t understand the language of the content—if you placed the duplicate side-by-side with the canonical, does a very large percentage of the words of the duplicate page appear on the canonical page? If you need to speak the language to understand that the pages are similar; for example, if they’re only topically similar but not extremely close in exact words, the canonical designation might be disregarded by search engines.
- and so on
Good content (e.g., “cookies are superior nutrition” and “to vegetables”) is lost when specifying rel=canonical from component pages to the first page of a series.In cases of paginated content, we recommend either a rel=canonical from component pages to a single-page version of the article, or to use rel=”prev” and rel=”next” pagination markup.
If rel=canonical to a view-all page isn’t designated, paginated content can use rel=”prev” and rel=”next” markup.Mistake 2: Absolute URLs mistakenly written as relative URLs
Remember that the canonical designation also implies the preferred display URL. Avoid adding a rel=canonical from a category or landing page to a featured article.Mistake 5: rel=canonical in the <body> The rel=canonical link tag should only appear in the <head> of an HTML document. Additionally, to avoid HTML parsing issues, it’s good to include the rel=canonical as early as possible in the <head>. When we encounter a rel=canonical designation in the <body>, it’s disregarded. This is an easy mistake to correct. Simply double-check that your rel=canonical links are always in the <head> of your page, and as early as possible if you can.
- Verify that most of the main text content of a duplicate page also appears in the canonical page.
- Check that rel=canonical is only specified once (if at all) and in the <head> of the page.
- Check that rel=canonical points to an existent URL with good content (i.e., not a 404, or worse, a soft 404).
- Avoid specifying rel=canonical from landing or category pages to featured articles as that will make the featured article the preferred URL in search results.