When building a new site from scratch or optimizing an existing one, webmasters face numerous decisions regarding many small details in SEO. It is no wonder that some of those details may be overlooked, such as the use of dashes and underscores in URL structures.
Many new website owners have asked—and still do ask—why such a minute detail matters in SEO. The answer is very simple: Google looks at dashes and underscores differently.
Google treats underscores as a joiner between two keywords, whereas a dash (also called a hyphen) signifies a separation of the keywords. For example, to Google, blue_shoes is just that: blue_shoes. In comparison, Google reads blue-shoes as blue shoes.
Therefore, if your URL contains “blue_shoes,” Google will only supply that page if the user searches for “blue_shoes”—which is very unlikely. If your URL contains “blue-shoes,” that page can be returned for the searches “blue,” “shoes,” as well as “blue shoes.″
This differentiation between the punctuation, according to Google’s head of webspam Matt Cutts, is a remnant from Google’s early days. Since Google’s original engineers were “techy” computer programmers, they were very focused on being able to find specific terms within the code. Using underscores made it much easier to find those files or macros within programming language.
The practice eventually carried over and evolved with Google’s search algorithm. Treating underscores as joiners is still in use with Google’s latest update Hummingbird, and Cutts said that the company had no plans in the foreseeable future to change how the search engine viewed them.
Although the difference between the two punctuation marks is great, Cutts explained that using dashes instead of underscores in URLs “doesn’t make that much of a difference” in relation to Google search results. It is a “second order effect” rather than a primary one.
Consider Wikipedia: the website comprises millions of URLs that contain only underscores and no dashes. But that does not affect Wikipedia’s ranking, considering that the website obviously does very well with the many other signals Google uses in determining SERPs.
Apart from Google, Microsoft’s search engine Bing does not differentiate at all between underscores and dashes as of August 2011. They are both viewed as separators.
If you already have a website that utilizes underscores in its URL structures, Cutts said it may not be worth the time and effort to rewrite all of them to include hyphens and create 301 redirects if the website is already ranking well due to other factors. Changing all of your website’s URLs could, in fact, create more problems than just sticking with the underscores. However, if you’re starting fresh and don’t yet have a foothold in search rankings, use dashes between keywords in all of your URLs.
From a user point of view, dashes also have greater visibility and usability. Underscores can be hidden by the link itself and appear as spaces, thus confusing the visitor. Consider these two URLs:
The underscore disappears into the underlined text, making it difficult for users to decipher the real URL and possibly link back to the website.
According to Google, dashes do trump underscores as the URL punctuation of choice. Matt Cutts’ video explained the difference between the two—which turns out is fairly great—but said that the effect of using underscores over dashes is relatively minor in search results.
That does mean that there is an effect. Imagine if Google proclaimed that all websites should unequivocally use dashes instead of underscores and that using the latter is detrimental. Cutts could have instructed website owners to change at least their top 100 pages, but that may have (and probably would have) caused chaos. Instead, Cutts assured the SEO industry that underscores are still OK.
Still, even if you have an established website, it might be worth it to actually rewrite your top 100 pages’ URLs if they utilize underscores. Google has come out in favor of the dash, although according to Cutts, they don’t influence much. But it could turn out, however, that using underscores has a greater impact than we know.
Jeff Williams is an SEO Project Manager at Fruition based in Denver, Colorado. Jeff uses his deep understanding of SEO and internet marketing to guide clients, optimize websites and ultimately improve search rankings.
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