by John Sherrod, Direc­tor of SEO

I work with a lot of ASP.NET websites and inevitably the issue of URL case sensi­tiv­ity and SEO rears its ugly head. It is not uncom­mon for a single URL to be artic­u­lated multi­ple ways in an ASP.NET website because it doesn’t affect the outcome of the page request. On Microsoft / Windows servers, /page1.html is treated the same as /Page1.html and /PAGE1.html. And I’ve heard it said many times “if it works, it’s right”.

Unfor­tu­nately, Google doesn’t subscribe to that philos­o­phy.

Google’s literal inter­pre­ta­tion of char­ac­ters and their case is precise, much like how pass­words work. That could be a conscious deci­sion but it also just happens to be how UNIX/Linux servers work (they’re customiz­able – so for the sake of simplic­ity, I’ll just call them all UNIX and move on). Microsoft servers don’t distin­guish between upper and lower case letters. UNIX servers do.

Not to get into the quality, stabil­ity and reli­a­bil­ity debate between Microsoft and UNIX servers, suffice it to say that they work differ­ently. If you’re devel­op­ing in PHP, you’re on a UNIX server. Because of the neces­sity of provid­ing exact match page requests to the UNIX server, it is much more diffi­cult to intro­duce dupli­cate content involv­ing differ­ent case URL struc­tures.

On UNIX, mis-matched URLs will simply break and the damage will be imme­di­ately appar­ent. It just won’t work. So if you have a page called /page1.php and you acci­den­tally link to /Page1.php, the server will respond with a 404 not-found error.

If your site is in ASP.NET then you are using a Microsoft server. In this case, /page1.html, /Page1.html and PAGE1.html will all be returned success­fully and will not break. In other words, requests for those URLs will resolve in a 200 ok server response indi­cat­ing, “All is well with those URLs”. So if Google indexes those 3 differ­ent URLs (and they will) they will see them as unique and inde­pen­dent.


Fortu­nately, in most cases Google is smart enough to even­tu­ally figure out that these unique URLs are really all the same page. Unfor­tu­nately, the flow of pageR­ank to each of those pages can be diluted or thinned because the various incom­ing links to those pages are not consol­i­dated. When this happens, rank­ings can actu­ally suffer.

To put it simply, 50 links to /page1.html and 50 links to /Page1.html is not equal to 100 links to /page1.html.

Several years ago, Google had a hard time distin­guish­ing between and if they both resolved with a 200 ok server response. That is prac­ti­cally a non-issue with Google today but can be a serious problem with Bing.

More recently, Google began to better under­stand that /page1.html and /Page1.html were just two instances of the same content. I don’t believe we will have to wait too long until the pageR­ank consol­i­da­tion of /page1.html and /Page1.html occurs in Google’s ranking algo­rithm. I can only guess that is some­thing on their radar.

However, don’t count Bing out of the race. Yes, Microsoft invented both ASP.NET and Bing but they are like wildly differ­ent siblings that just happen to have the same parents. Bing is picky. Bing likes a defined Canon­i­cal, light code, clean archi­tec­tures and pages that are named, tagged and opti­mized with keywords. And even though Bing uses their own servers (one would assume) their CDN is actu­ally Akamai, which runs on Linux. But I digress.

So, back to the ques­tion – Is case impor­tant in URL struc­tures when it comes to SEO? Yes, it is.

At a funda­men­tal level, search engines need to clearly under­stand the differ­ence between bird the animal and Bird the nick­name (Charlie Parker) and Larry Bird the legendary basket­ball player. Capi­tal­iza­tion matters because the intent is differ­ent. And intent is that little nuanced piece of love­li­ness that search engines constantly strug­gle to deter­mine about its users. They are good at it, but not great.

So don’t leave it up to the search engines to try and deter­mine your intended struc­ture. That’s just more work for them to do and history says they can and will get it wrong. And that can cost you or your client’s money when it comes to SEO.