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You shouldn't plagiarize content from other sites, obviously. But why is duplicate content penalty-worthy if 1) it all belongs to you and 2) you aren't trying to manipulate search engines?

I mean, who cares if both "www" and non-"www" versions of your site work? Can someone please explain why "minor" duplicate content is considered bad?

marked as duplicate by Stephen Ostermiller Aug 22 '18 at 17:31

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    Ironically this is a duplicate question. As the answers in the duplicate explain, Google doesn't penalize for internally duplicated content. The duplication has to be plagiarism and spammy to get a full site penalty. – Stephen Ostermiller Aug 22 '18 at 17:34
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    Fixing duplicate content such as www and no-www could help with rankings. The less duplication you have, the better for rankings. You basically want all your links pointing consistently to your preferred URLs. This is much less of an issue these days than it was 10 years ago. Google is doing a much better job automatically managing common duplication scenarios than it used to. – Stephen Ostermiller Aug 22 '18 at 17:38

Google penalises duplicate content for two reasons:

  1. Duplicate content (across different domains) suggests that you don't own the content, or that you copied the content
  2. Duplicate content has a negative effect on the user experience

Having both www and non-www version of a website won't result in a penalty, Google will likely just choose one version to show and demote the other. This is to improve user experience where access to both versions adds no value.

A more subjective reason that SEOs advise against duplicate content is the message that is sends to Google. Google is trying to decipher the specific order or relevance for every website against every search phrase. One way that it makes this decision is by looking at how well optimised (see Why is loading speed of a website important for SEO?) and cared-for a site is. Having duplicate content tells Google that your website is not especially looked after and therefore may actually be less authoritative - of course with most things SEO-related this is just speculation, although there have been a number of tests to support this theory.

So to clarify:

  1. Minor duplicate content is not bad if it doesn't effect the user experience
  2. You won't receive a 'penalty' due to a lack of a 301 redirect between www and non-www
  • "Duplicate content suggests that you don't own the content, or that you copied the content" - this is not true. You seem to be assuming that most, of what is considered "duplicate content" is cross-site; it is not. Most "duplicate content" (and what Google reports as "duplicate content") is internal to the website and is simply when you have more than one URL on your site that returns the same or similar content. This can be as simple as /foo and /foo?sortby=date. This does not necessarily have a negative effect on user experience and there is no actual "penalty". – MrWhite Sep 4 '18 at 15:29
  • @MrWhite Thank you for your valuable feedback (and for the downvote). I have edited my answer for clarity. – Double Clicked Sep 4 '18 at 15:52

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