What are canonical URLs and how do they affect your SEO? [closed]

Question

I've heard people mention the Canonical URL tag, but I don't know what it means or what its purpose is.

What is it and how does it affect SEO?

Comatose

Answer 1

Canonical URLs are used when you would otherwise have different URLs that point to the same content without actually redirecting. So let's say your domain is example.com; www.example.com and example.com are two different URLs, and if you don't redirect them to a standard (canonical) URL (for instance, example.com), search engines treat the two URLs as completely different pages. This causes the link popularity of the two URLs to be split, which is obviously very bad for SEO.

Alinaaline

@musicfreak, if you can incorporate some of the info from those URLs into your answer it would be for the best. External links die, decay and we are attempting to have a comprehensive knowledge base here. – Toby

One of the huge reasons for wanting to use Canonical URL's is if you have 2 different URLs pointing to the same content then their search value/weight can be split up between them. Because it is split up between the two URLs it can lower the position your results are shown. – Toby