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I want to purchase a second level domain (on the web platform Altervista.org) with the .com extension. Since within the domain verification process I can type characters in both upper and lower case letters, I wonder if this may affect the final form of my domain, in the sense that I wonder if in the URL the characters will be displayed in upper and/or lower case letters, according to my previous choose.

Just to be clear, let's suppose, for instance, that I want the name "MyWebSite" and during the domain registration process I choose "MyWebSite": will the final URL be www.MyWebSite.com or www.mywebsite.com?

So, my question is: can a domain name be displayed both with upper or lower case letters in the URL and in the search engines results, according to the webmaster's previous choice?

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Simple: Show me 1 domain which does. Screenshot without changing anything please ;) – Martijn Feb 25 at 8:16
Martijn is saying that it can't be done. You've never seen an example of a domain that has done this because it isn't possible. – Stephen Ostermiller Feb 25 at 10:45
I'm wondering whether specifying the case of the domain name in canonical tags, or issuing redirects based on the case of the domain name would be effective. – Stephen Ostermiller Feb 25 at 14:53
This question was covered in a very detailed answer found here: webmasters.stackexchange.com/questions/90339/… It is well worth a look!! – closetnoc Feb 25 at 16:27
up vote 18 down vote accepted

No, it will not affect the final letter case format of your domain whatever letter case you choose while registering it.

The Domain Name System (DNS) names is case insensitive and you can not manipulate this by any mean when you register it or even define it to search engines for "good looking" purposes.

All cases (upper and lower) will be accepted when you type it on your browser or your FTP client software or your email client software or your links.

You can read all the Case Insensitivity Clarification for the DNS standards on Internet Engineering Task Force website

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thanks. That "upper case will be accepted when I type it on my links" does mean that I may chose upper-case letters when I'll create my links (is it meant to be done later manually, is it right?) or should I type them right now, while registering the domain? – robertalrp Feb 25 at 8:29
You can make your domain whichever letter case you may like in your html code for your links but that will not affect what it will show in browser's url bar, which will be lower case display of the domain name. However everything that goes after your domain it is definable by you (www.yourdomain.com/MySubFolder/INdex.html) – Vasilis Kosmas Feb 25 at 8:34

Whilst DNS itself is case-insensitive, at least one search engine allows you to declare preferred case in search results: Yandex.

Yandex - Case of the site name

The Case of the site name tool lets you set preferred capitalisation in certain cases. This can be accessed in Yandex.Webmaster under Appearance in search results > URL letter case.

I've set this for a few of my sites and it's quite nice to see.

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As well, some search engines including Google would take recognized terms from their ontology and apply title case to the domain name. This was done to help the SERPs perform well. I have not looked lately to see if this is still done. – closetnoc Feb 25 at 16:24

Well technically you can register your domain in any case. But for the record, no matter how you type your domain in the browser it will transform to small case. This is because DNS is not case sensitive.

If it makes sense... www.YAhOO.com should be no different to www.yahoo.com or www.yAhOo.com... You can play around your browser's address bar and see what happen.

This link should be able to help you understand the concept further.

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As the other answers stated, DNS is case-insensitive, however that hardly matters here. You can serve HTTP 404 pages for some requests and HTTP 200 pages for others from the same IP.

You can check the Host HTTP header and server different content based on the capitalization of it. You could serve a 404 page or a redirect if the capitalization isn't correct.

However, AFAIK, all common browsers will convert the domain portion of a url to lowercase (probably to protect against registering domains with similar looking characters, like I (capital i) instead of l) and also send an all lowercase value for the host header, so you would end up with an infinite redirect in browsers, but there is nothing in theory, about HTTP that prevents you from doing it. It is a browser limitation.

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No. You can't. This isn't possible. DNS is case insensitive.

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Can you give some backing evidence for that? One-line answers aren't overly helpful. – Andrew Lott Feb 25 at 14:39

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