: Would the following URLs result in duplicate content if I only used one canonical link? In your experience, have you ever had problems with duplicate content being caused by the following URLs:

@Eichhorn148

From a technical standpoint, only two of those are actually different URLs. The following are always the same:

www.example.com http://www.example.com/


The reason is that it is impossible for your site to serve different content at those two URLs because of the way that the HTTP protocol is defined. When a request to your server is made, the first line looks like:

GET / HTTP/1.1


Where the slash is the the part after your domain name. The HTTP spec does not allow this to be empty, so a browser must send a slash when fetching www.example.com.
This is in contrast with

www.example.com/path http://www.example.com/path/


which could have different content because they look different when your server receives them.

Because clients always send a slash, I prefer www.example.com/ as the canonical URL because it best matches what actually happens under the hood.

Your canonical element should prevent search engines from indexing duplicate content, or penalizing for it.

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@Samaraweera270

No, not if their content is identical (or very nearly so), and they all have a canonical link element referencing mysite.net.
However, that sort of issue happening site wide can be considered a crawl efficiency issue and the canonical link element doesn't really solve that. In your example, a search bot would crawl three pages when it really only needed to crawl one. Scale that up, and add other duplication issues, and it gets to be a problem.

So for that sort of issue (we can include things like with/without the www subdomain, with/without HTTPS, etc.), it's usually better to use URL rewrites to 301 redirect back to the canonical form.

The canonical link element is the weapon of choice when there's a lot of variation in the duplications you're managing, or you don't know in advance what they will be. Think of a shopping site where tens of product category refinement parameters can be added to a base URL in any order, for example. That doesn't mean don't add it unless you have that sort of problem, just don't rely on it to solve problems there are better solutions for.

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