Maybe I got a little carried away on this one, but I’ve seen so much garbage about this across the Web that I feel compelled to set the record straight with some evidence. Evidence in SEO is something that most folks fail to provide when they make claims. So, part of the reason I started this blog was to run counter to the unfounded heap of SEO advice that the web is awash with. If I can’t convince you with my posts, then I probably won’t even bother to try.

There are good reasons to use a hyphen when naming files on your web site. Google treats underscores as “word characters” which means that it is an extra alpha character in the a-z A-Z range. Imagine that it is a new character that follows the letter Z and that any time it’s used, it is essentially like placing another letter in a series of letters, so that “the_real_deal” becomes one word instead of three, and really becomes nonsensical as such. The same thing happens with your file names if you use underscores. Hyphens are treated as “non-word characters” by Google, so that when you use a hyphen between the words in a document name, Google parses out each word as if the hyphen were a space. Here are some compelling reasons to believe that you should hyphenate or die:

Underscoring the Underscore with Scorn

The Real Deal with Hyphenation

The Version without Hyphens or Underscores has the Same Results and the Hyphenated Version

Here’s a case where a picture is worth way more than a thousand words. How about 101,000,000 results for the-real-deal compared to 91,000 for the_real_deal. Notice how the hyphenated search returns dictionary linked terms for real and deal? The underscore version doesn’t because Google does not read it as three words. If Google doesn’t read your query as three words, do you think you’re document names will be seen differently? That wouldn’t make sense would it?

It that’s not enough to convince you, maybe Mr. Cutts can:

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