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Let's say I have a product/brand with a website, for the purpose of this question the product is called Acme and the site is http://acme.com .

  1. What's more correct when referring to the site without an hyperlink? For example, in PR:

    • Acme.com
    • acme.com

  2. Does it make any difference if I'm using it inside an article's caption? For example:

    • You’re invited to the launch of Acme.com!
    • You’re invited to the launch of acme.com!
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    On a technical note, DNS is case-insensitive, so it doesn't matter what case the letters are when the user types in the domain name; it should resolve to the same IP(s).
    – Jez
    Sep 14, 2011 at 10:20

8 Answers 8

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Editor of the Jargon File here. If there is an authority on this question, I'm it.

Never capitalize domain names unless you know for certain they were registered with that exact capitalization. In practice this means: Never, ever capitalize. If these means you have to rewrite a sentence to avoid having a domain name at the beginning, do so.

The more general rule, which explains this one, is: never capitalize any name with a case-sensitive encoding. Other cases this includes are variable names in mathematical formulas and computer programs, and names of programs on operating systems (like Unix) with case-sensitive filenames.

(Some people will reply that domain names are not case-sensitive. In the new Unicode world this is no longer true. And even in older times, interfaces that expected domain names - including embedding in URLs - were often case-sensitive.)

The reason for this rule is that you never want to mislead humans into remembering and using a case variant that a literal-minded computer will not accept.

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    If unicode domain names are not case-insensitive, how is a person supposed to know if a domain was registered in any particular case? The registrars I've dealt with register domains in all upper-case but I've never submitted a domain in anything but lower-case.
    – Mr. Shiny and New 安宇
    Sep 14, 2011 at 2:06
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    Most registrars don't do Unicode yet, which is why they still register in all uppercase. It would be unwise to count on this continuing. Knowing the actual case the user intended is a marginal, theoretical possibility; that's why I said in practice, never.
    – ESR
    Sep 14, 2011 at 11:43
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I don't think there is a correct answer for this question. It's a matter of style: you decide what to do each time.

I've googled 4 famous brands and visited their page on Wikipedia, their websites were written like this:

  1. Site.com
  2. site.com
  3. www.site.com
  4. http://site.com

As you can see, everyone adopted a different format. It might depend on the site's specific URL, but putting that aside, in the first two the choice for the capitalization is not on "correctness".

Just a note: If you write it one way in a document, keep that logic everywhere in that document. This would be the only rule: be consistent in your own writing.

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    Thanks. One interesting fact is that Facebook capitalize their name when they use it as a name for the service/company (although the logo reads facebook) and wherever they write their domain name, they write facebook.com and not Facebook.com.
    – Ofer Zelig
    Sep 13, 2011 at 11:48
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    Domain names are inherently case-insensitive and practically never written with capitals. As far as I can see, the Facebook case is uninteresting: it is simply adopting the usual convention.
    – Neil Coffey
    Sep 13, 2011 at 14:09
  • @Ofer Zelig I've noticed similar usage for certain Google products. It is very confusing to me.
    – Ellie Kesselman
    Sep 13, 2011 at 14:27
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    Oh wow, my hero @Neil Coffey This man is a java and encryption legend! Here, of all places. I've even blogged about you. Beg to differ re case-insensitivity though. That's what I USED to think, until I read a post by Google about this. Domain names SHOULD be case insensitive per IETF or W3C whatever, but... I'm off topic, I'll try to find link about this, leave it in ELU chat room for y'all.
    – Ellie Kesselman
    Sep 13, 2011 at 14:30
  • @down-voter, care to explain? :)
    – Alenanno
    Sep 16, 2011 at 13:40
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From an IT standpoint the generally observed customs are:

  • As a general rule domain names are written in lower case.
    This transcends other conventions like capitalizing abbreviations/"initialisms" - for example the IANA website is referred to as "www.iana.org"
  • It is preferable to let the domain name stand alone the way you would type it in a URL bar.
    For example "The new acme.com website" rather than "acme.com's new look"
    This one is not universally observed, and is often disregarded if the possessive form "sounds better".
  • Avoid starting sentences with a domain name (to avoid the capitalization issue)
    (A simliar convention is observed when discussing operating system commands that are case-sensitive.)
  • In marketing documentation it's acceptable to capitalize the domain name in a manner consistent with the brand (e.g. "Acme.com", "PremierHeart.com").
  • If it is included as part of the domain name "www" is written in lowercase, not as "WWW" and under no circumstances as "Www" (which looks utterly ridiculous).

That said, as others have pointed out it's probably more important to be consistent.

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  • It sure seems like using WWW would be valid since it is an initialism and those are typically capitalized. (WWW = World Wide Web) I agree Www would never be the right thing, www is so common that it can't be wrong.
    – Zoredache
    Sep 13, 2011 at 22:20
  • I have a hard time accepting WWW only because it looks awkward (capitals, period, lowercase/CamelCase/etc.), also it's not something I see much around here. That said it's infinitely more correct than Www and I'm more than happy to grin and bear it if it shows up in copy.
    – voretaq7
    Sep 13, 2011 at 22:22
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    @Zoredache: IMO, it is correct to use WWW as an initialism outside of URL, but you should never write WWW.google.com.
    – Lie Ryan
    Sep 14, 2011 at 3:48
  • +1 for the mention of marketing. It is even more important with domains that are made up of multiple names/words, now that hyphens are no longer used in most modern domain names.
    – Guy Schalnat
    Nov 18, 2015 at 15:35
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There is an important distinction to make here.

One, a domain name is traditionally written in lower-case even though it is case-insensitive. So if you are writing a URL (or a domain name that is meant to represent a url) you should probably write it in lower-case.

If you are writing the name of a company, or a product, or some other proper noun, that proper noun will have its own rules of capitalization. So you'd write Sony but not Sony.com.

Some companies are named the same as their domains. In this case there might be different rules depending on whether you are referring to the domain or to the company. The company itself might request that you always write both names the same way, even if that means upper-casing a domain name. However, I don't think it's incorrect from a style perspective to always lower-case web addresses.

The most important thing is to be consistent.

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  • +1 "some companies are named the same as their domains" (though I can't think of some really well known examples: Pets.com is defunct and del.icio.us is apparently now called Delicious. I know of chess.com.)
    – RoundTower
    Sep 13, 2011 at 23:25
  • @RoundTower. The most famous example is probably Amazon.com.
    – TRiG
    Sep 14, 2011 at 0:33
  • @TRiG: Glad you mentioned Amazon. Look at their site. The site's title (the browser's top bar) reads Amazon.com: Online Shopping... which I can definitely understand by the way, since Amazon.com is used as the first word of the sentence. But their logo is amazon.com - lower cased.
    – Ofer Zelig
    Sep 14, 2011 at 6:22
  • Amazon is not a great example: the company is indeed incorporated as amazon.com, Inc. but even its own press releases, e.g. this one often refer to it as Amazon and keep amazon.com to refer specifically to the US-facing site. Pets.com, on the other hand, would never be referred to as Pets.
    – RoundTower
    Sep 14, 2011 at 9:15
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For brands and trademarks, there is no rule on how to write it; the owner of the trademark or who can legally use the brand decide how it is written. For example, there is the Apple iMac, which is not written Imac, and Mac OS X is not written Mac os x.

In the case of a domain name, there is generally associated a trademark; for example, stackoverflow.com is associated with Stack Overflow. In those cases, I would use the second one.

You're invited to the launch of Acme.
You are invited to the launch of AVPnet.

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  • I guess you are right. When I asked my original question, I was seeking for an answer whether there is a "standard" or a clear English rule regarding that matter, or is it subject to personal preference.
    – Ofer Zelig
    Sep 13, 2011 at 11:51
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    Well, ALL orthographical rules are human inventions and subject to personal preference. I'm not sure why you worry about this too much. If you put down your grammar book and have a look at some actual web sites, I think you'll find that domain names are practically never written with capital letters.
    – Neil Coffey
    Sep 13, 2011 at 14:11
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    Why should owners of trademarks decide how other people must write them? I refuse to bow to their will. I don't see why regular rules of style shouldn't apply here as well.
    – Cerberus_Reinstate_Monica
    Sep 13, 2011 at 17:10
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    @Cerberus That is valid also for the name of a person; if somebody decides to call his son Alberto (even if he lives in USA) or Aldbert, there is nothing wrong with that. Are you going to call that person Albert just because in English that is the name? :-)
    – apaderno
    Sep 13, 2011 at 17:17
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    @Cerberus It's not about etiquette, but convention. If you write i am, and you are not a native speaker of English, you could be taken as somebody who doesn't know much of English; if you write Iphone you could be probably taken as somebody that doesn't know much about Apple and its products. In the case of trademarks, there is a difference between I phone, Iphone, and iPhone; if you have the copyright on one of them, you don't probably have the copyright on the others too.
    – apaderno
    Sep 13, 2011 at 17:34
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I would say "Acme.com" would be a more correct term. This is because "Acme.com" is a proper noun. A proper noun is defined:

A proper noun or proper name is a noun representing a unique entity (such as London, Jupiter, John Hunter, or Toyota), as distinguished from a common noun, which represents a class of entities

If you were to say, "You're invited to the launch of our website", website would have been a common noun, and thus, not capitalized.
However, "Acme.com" is a proper noun because it represents a unique entity.

Thus, I recommend writing:

You're invited to the launch of Acme.com!

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    Also iPhone is a proper noun, but you don't write Iphone.
    – apaderno
    Sep 13, 2011 at 9:44
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    camel case (frequently written: camelCase)
    – Ofer Zelig
    Sep 13, 2011 at 9:47
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    Except that domain names are not case-sensitive. You seem to be assuming that a domain name must adopt the orthographical conventions of an ordinary sentence, but there's little reason for this assumption.
    – Neil Coffey
    Sep 13, 2011 at 14:04
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    @Neil The fact that domain names aren't case-sensitive is why you're free to capitalize them as you see fit, following a chosen convention convention (for instance capitalizing the first-letter as a proper noun, or camel-casing to make them more easily read).
    – GAThrawn
    Sep 13, 2011 at 14:19
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    Note that while domain names are case-insensitive, the remaining parts of a URL generally aren't.
    – hammar
    Sep 13, 2011 at 16:58
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If your domain name is prone to ambiguous reading, you may want to capitalise it: ExpertsExchange.com, PowergenItalia.com, etc. Otherwise, it's probably not worth doing.

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I think that the context in which you write the domain name does make a difference. For example, if you're writing an article about the company Acme, then it may be acceptable, depending on style, to refer to their website in the article as Acme.com, because in this context the URL is acting as just another trademark or piece of branding. But if your article is primarily about the website, its functionality or implementation, then I think that @ESR's answer is more pertinent since the URL now has a specific technical meaning, and should be capitalized only if you know that it was registered that way.

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