Remove Underscores in URLs
Why Remove Underscores?
For years, Google and other search engines have considered the underscore to be part of a word. So, search terms like REMOTE_ADDR can be easily found in the search results. Of course, the URL has also been a factor in determining search engine results placement. Granted, it is not exactly a huge factor, but it can carry some weight. This is precisely why we can Google search a domain name, and the URL with the domain name ranks first in the search results. After the domain name, the URL starts to display keywords with folders, file names, and parameters. Consider a URL like www.example.com/articles/improve_my_website/. From the URL, we can see that the web page is an article about how to improve my website. While search engines agree that this is probably an article, they don't all believe this is about how to improve my website. This URL contains underscores in the last keyword phrase. My intention was to highlight the keyword phrase "improve my website", but Google will only see it as "improve_my_website". The probability of searchers separating words by underscores as opposed to spaces is highly unlikely.
Use Hyphens in URLs Instead
You have probably seen many URLs that have keywords separated by hyphens and not underscores. You might even notice that websites that are more popular use this standard. Well, that is because search engines see the hyphens as being more like a space. When you were first learning English, you were most likely annoyed by the random exceptions and cases of the language. Separating words with hyphens is no different. Without consulting a dictionary, an average person will stumble on when and how to use a hyphen to separate a phrase. As always, the grammar police try to offer a hyphen explanation to our odd language. Despite the annoying grammar police, Google and other search engines appear to always replace the hyphen with a space. Try googling for something like "good-looking art" and compare the results against "good looking art". The results should be exactly the same. So, if Google considers an underscore part of the word or phrase and replaces the hyphen with a space, it makes sense to use hyphens to separate our keywords or keyword phrase.
Conforming to URL Standards
These two URLs have a fairly similar level of readability. The underscores and hyphens can both be interpreted by a user as a space separating words. However, the best practice on the web is to use hyphens, which really gives a website no solid reason not to use underscores instead of using hyphens in the URLs to highlight the keywords or keyword phrase.