Google’s John Mueller recently stated that self-referencing canonical tags are not absolutely necessary, but they do help.
In Mueller’s words: “It’s a great practice to have a self-referencing canonical but it’s not critical.”
This topic came up during a recent Google Webmaster Central hangout when a site owner asked about the importance of using self-referencing canonicals.
Canonicals are typically used to link a non-canonical page to the canonical version, but they can also be used to link a page to itself.
Self-referencing canonicals are beneficial because URLs may get linked to with parameters and UTM tags.
When that happens, Google may pick up the URL with parameters as the canonical version. So a self-referencing canonical lets you specify which URL you want to have recognized as the canonical URL.
Google recommends using self-referencing canonicals as a best practice, but they’re not required in order for Google to pick up on the correct version of a URL.
Hear Mueller’s full response in the video below, starting at the 28:53 mark:
“It’s not critical to have a self-referencing canonical tag on a page, but it does make it easier for us to pick exactly the URL that you want to have chosen as canonical.
We use a number of factors to pick a canonical URL, and the rel-canonical does play a role in that.
So, in particular, things like URL parameters, or if the URL is tagged in any particular way – maybe you have links going to that page that are tagged for analytics, for example – then it might happen that we pick that tagged URL as a canonical.
And with the rel-canonical you’re telling us that you really, really want this URL that you’re specifying as the canonical…
So it’s a great practice to have a self-referencing canonical but it’s not critical. It’s not something that you must do, it’s just something that helps to make sure this markup is picked up properly.”