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Is there any specific reason to why stackoverflow isn't using www in their URL? When you type the site change it to This is opposite to what many other sites does. I like it, and I can see it is useful since the URLs these days are long and contains a lot of navigation information. Is there also a SEO advantage?

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up vote 13 down vote accepted

Is there also a SEO advantage?

No there isn't.

It's really a matter of preference, do note though that omitting the www has the huge disadvantage that you can't create a cookie for the current domain only (as a cookie with "" would be interpreted as domain-wide, including subdomains like "").

For this reason I personally prefer to use the "www" for my websites but, again, it's just a matter of preference :)

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And I guess Jeff et al regret this choice a bit: Dropping the WWW Prefix (June 2008) was followed by the introduction of the cookie-less in A Few Speed Improvements (August 2009). – Arjan Apr 2 '10 at 10:26
Besides the cookies, using different (sub-)domains also helps Maximizing Parallel Downloads in the Carpool Lane. – Arjan Apr 2 '10 at 10:30
That's not actually true, is it? (Not really my area.) – Tom Hawtin - tackline Apr 2 '10 at 18:43
@Tom: what isn't? Everything I said is true. Everything Arjan said is true. – Andreas Bonini Apr 3 '10 at 1:42
It wasn't a reply to Arjan. You can set a cookie on a particular host name, and not include host names which it is a postfix of. You can even go finer grained than that. – Tom Hawtin - tackline Apr 3 '10 at 20:34
@Tom: no you can't, if you set a cookie to "" it will be active on all subdomains too. – Andreas Bonini Apr 4 '10 at 4:18
@Tom, Use Cookie-free Domains for Components: If your domain is, you can host your static components on However, if you've already set cookies on the top-level domain as opposed to, then all the requests to will include those cookies. In this case, you can buy a whole new domain, host your static components there, and keep this domain cookie-free. Yahoo! uses, YouTube uses, Amazon uses [..]. – Arjan Apr 4 '10 at 9:55
@Arjan – Tom Hawtin - tackline Apr 4 '10 at 10:03
@Tom, I didn't read that RFC, but if that claims otherwise, then apparently many browsers behave differently? (Or many servers use a different mechanism?) – Arjan Apr 4 '10 at 10:30
@Arjan: indeed that's the case. RFC and standards are cool and everything but they are irrelevant if browsers don't follow them; you shouldn't use "" as your cookie if you don't want it available on subdomains for the same reason you shouldn't use display: table-layout (but doing the former is much more dangerous: the website won't work at all if a subdomain tries to use a cookie already used by the domain for a different purpose) – Andreas Bonini Apr 4 '10 at 11:08
@Kop Seems like a rather naughty IE bug. There's a thing. – Tom Hawtin - tackline Apr 4 '10 at 14:15

As @Kop suggests it's primarily personal preference. From a historical perspective, the www prefix was de rigeur early on in the web to distinguish the host performing web service from other common services (ftp, smtp, gopher, ntp, dns, ...) and many organizations followed a naming scheme on their highest level domain with these common names to make it easier to determine where the service was located. Typically this was an alias for the real system name, usually something like doc, sleepy, or grumpy (if the admin was in a Disney mood the day the first one was installed). Not all organizations did this, but enough so that it became a defacto standard -- there may even be an RFC recommending this, but my memory is fuzzy.

As the web became the dominant paradigm for the publication and exchange of information, though, the use of the other protocols, while not dwindling, became important to a smaller and smaller fraction of the people actually using the web. -- As an aside, do you know that there was a time when you could (and might actually have to) type in the full path that your email should take to get from your system to the mail system of the intended recipient? -- Browsers, in fact, changed to add the www prefix if you omitted it and it couldn't get a response to the prefix-less name from the name server. At that point the utility of using the prefix to distinguish the purpose of the host in question became much less valuable and the usability of having the prefix-less domain name be given to the web server host dramatically more important. Most organizations support both (not, however, the university where I work) and because users have gotten used to the prefix-less name, many organizations have adopted the prefix-less name as the default -- partly because this saves at least one round-trip name lookup if you don't.

In my case, what I typically develop are services or web applications. I prefer the semantic value of using the service name over the prefix. It helps the user to remember what the name is and the prefix doesn't (actually in any case) add any real value to the end user; it's just more characters they have to type if they don't let the browser do the automatic expansion.

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See also

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or if your looking for a laugh – Earlz Apr 3 '10 at 18:31

Your question has already been excellently answered. What I always like to add when there's a "www or not?" discussion is that most users have become accustomed - by relentless use in advertising and media in general - to recognize a web address by the www. prefix. I often encounter expressions of surprise that there even are web addresses that don't start with www.

So from that point of view, if you are targeting normal end-users, I'd recommend to use the www. prefix, and a TLD that is widely known in the target market(s). In the US, that would be .com, in the UK .com and, in Germany .de and so on and so on.

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Whoops, this is Meta! I thought this was an SO question. Well, I'll let it stand anyway. – Pëkka Apr 2 '10 at 12:02

Jeff doesn't think it matters whether you have the dubya-dubya-dubya, so they probably probably spun a coin to decide.

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To your actual question, as pointed out by Arjan, it was a preference move:

So, for stackoverflow, we’re going with plain old, and dropping the www prefix.

For the soapbox side, it does help with SEO over possible duplicate content issues where search engines may see the and domains as dissimilar.

Even Google asks you which version the site should be under:

Preferred domain (www or non-www)

The preferred domain is the one that you would liked used to index your site's pages (sometimes this is referred to as the canonical domain). Links may point to your site using both the www and non-www versions of the URL (for instance, and The preferred domain is the version that you want used for your site in the search results.

So yes, there is an SEO advantage if you stick with one version.

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The problem of duplicate content you are referring to occurs when both and display the same exact website, without redirecting to the preferred URL. This is however irrelevant to the choice of vs vs which is what the OP asked (there is no particular SEO advantage of using one form over the other). Additionally all pages of SO have a rel=canonical <link> so even if duplicate content was to be displayed it wouldn't matter. – Andreas Bonini Apr 3 '10 at 1:38
You should read the question for the first time, which is why did Stack Overflow choose no-www over www. And point out where the OP is asking for a personal rant. @kop – random Apr 3 '10 at 9:25

Someone is using a web browser with a URL starting with http:// (or better https://), and they are not sure if they are on the world wide web? Putting www. in there indicates that you think your readers are thick.

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Those people probably don't know there's a thing called the "world wide web", let alone what the difference to the "internet" is. – balpha Apr 2 '10 at 18:51
There's no nice way to answer this one... – Paul Nathan Apr 2 '10 at 22:08

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