Are URLs Case Sensitive?
In many cases, yes. Some servers (like Microsoft/IIS) you won’t have an issue with, but others (like Linus/UNIX) might make a distinction between an uppercase and lowercase character in a URL.
Do Capital Letters in URLs Affect SEO?
Case sensitivity in URLs only becomes an issue for SEO when (or if) multiple versions of your URLs get found by search engines. If the URL doesn’t automatically resolve to a version without capitals, and you have shared links that sometimes include capital letters and sometimes don’t, then you are going to start having a problem.
Search engines crawl the individual pages of your website and assign trust and authority to each of these based on many factors (including links to your website). If, for example, you have two pages for every page of your website, you would be sharing the trust and authority assigned between two, rather than consolidating it all into the one version of each page.
To maintain the strongest, most authoritative domain and page possible you want to avoid diluting your authority (sometimes known as ‘link juice’) by having duplicate content.
The problem with case sensitivity is:
is technically (in the way Google treats it) a different page or piece of content from:
As I’m sure you can imagine, this could create endless duplicate versions of each page on your website. This could potentially dilute the authority of any page by many hundreds. This would be bad news for any website.
Of course, it’s unlikely to get that bad. It’s much more likely to be diluted by one or two, if any at all, but it’s something that’s better to cover off and sort out early. If an issue does develop it could get nasty and why risk that? It’s going to be much harder to fix retrospectively so the risk is not worth taking.
What Else Can Case Sensitivity in URLs Affect?
Along with the page authority of your pages and authority of your website as a whole, URLs including uppercase letters are also likely to be reported separately by Google Analytics and, as mentioned above, might end in 404 errors on the wrong server.
How Can I Stop Case Sensitivity Problems?
If you have case sensitive URLs, there are a couple of options for you. You’ll want to either automatically 301 redirect URLs using the incorrect case (any uppercase letters) to the lowercase version or use the rel=canonical tag to indicate to search engines which one is your preferred version.
A 301 redirect would be preferable. You should be able to redirect a few pages (if it’s a small issue), or you could set a site-wide redirect instead. A site-wide fix is probably your best bet to prevent any issues arising in the future.
There’s a few different methods – this great blog from Alex at inflow (http://www.goinflow.com/redirect-uppercase-urls-to-lowercase/) talks through some of your redirecting options.
I would avoid using canonical tags, if you can. 301 redirects are much more likely to address the issue fast and more effectively. If you have no other choice, however, then a rel=canonical pointing back to the lowercase version of the URL is better than nothing at all.