The duplicate pages are bad in SEO (Search Engine Optimisation). They bring down your page rank scores. Duplicate pages have similar or even identical contents. For example, different styles, HTTP or HTTPS, www or non-www etc. These pages usually serve the same content, and you should ensure the search engines only index 1 copy for all similar pages.
Ensure a 301 Redirect
A 301 redirect tells the search engines that this page is permanently redirected to a new page and the page score should be transferred to it as well. It is useful when you are migrating to a new domain, starting using the HTTPS version, or deciding to use www or non-www URLs. Remember, the search engines treat HTTP and HTTPS two different copies unless you tell them not to. Search engines storing duplicate contents are bad because the scores will be split among these pages as well. For 301 redirection, the targeted URL will show in the browser, so it means you just have to maintain a copy of the version. Therefore, it is not suitable if you intend multiple versions accessible e.g. www and root domains, HTTP or HTTPS versions.
Unnecessary Index Tag
By default, the search engine bots follow the principle:
<meta name=robots content="index,follow"/>
It means, that the bots will index the page and follow every links found on it. If you are not changing the default behavior, don’t need to put this rule in the head tag.
NoIndex But Follow
It is almost true that you should do a noindex but follow when you dont want a similar page get indexed. When a page is removed from the search engine indices, the other meta data can be ignored/excluded, for example, the tag: keyword and description.
SEO improvements
The meta tag NoIndex is supported by most search bots, e.g. GoogleBot, Yahoo Bot. It is a good place to use NoIndex on the duplicate pages that only differ in styles (e.g. mobile version or desktop version). You can also use them on low-value pages such as forum index pages.
Canonical
You can specify the following syntax to hint search engines the original/genuine URL:
<link rel=canonical href="https://helloacm.com/" />
Remember, this is only a hint and the search engine may still index the page. The Canonical tag may not be supported by all search bots so don’t rely on them. So the use of Canonical and NoIndex is for the opposite purpose. The Canonical hints that this page should not be indexed unless the target URL is itself (self-Canonical). The NoIndex explicitly tells not to index the current page. So you just have to pick one and don’t send the mixed signal, which may cause trouble if the target Canonical URL is NoIndex.
If the page has Canonical and NoIndex, some search engines might NoIndex the target Canonical URL even it is to be indexed because the search engines might think that the two pages should be equivalent. It depends on how the search engines interpret the Canonical keyword.
So here is the rule:
On indexed pages, use Canonical keyword. On non-indexed pages, use NoIndex. Click To Tweet–EOF (The Ultimate Computing & Technology Blog) —
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