It's a time-tested method used by virtually all SEOs making a plunge into the world of link building – directory submission. For the most part, it's not excessively expensive, doesn't take a lot of time, and if you submit to the right directories (read: ODP and Yahoo! Directory), it can have a meaningful impact on your website search engine ranking.

Despite its allure, however, excessive reliance on directories for building your website backlink profile can backfire. Submit your website into too many low-quality directories in too short of a time frame and you'll get flagged by Google. That of course begs the question: how exactly does one evaluate the quality of a link directory? To make the process a bit easier, our team put together a list of five easy (and free!) ways of ensuring that you are only submitting to directories that will have an impact.

Hello? Is anyone there?

One of the defining traits of a quality directory is the presence of human editors, i.e. real people who manually review every submission. Directories that auto-accept URL suggestions are much more likely to contain low-quality websites that degrade the value of the directory as a whole, both in the eyes of search engines and its human visitors. Most directories that have editors on staff make the point of stating so right on the homepage. Consider it a "seal of trust" of sorts. If that fails, look for an "About Us" page.

Can I get some juice?

Although a well-built backlink profile consists of both nofollow and follow links (the former are recognized by search engine spiders but do not have an impact on rankings), if you are taking the time to submit your website to a link directory, you might as well make sure that the link is passing juice, i.e. it will have an impact on your search engine ranking. To check, view the website source code and look at how the hyperlinks are set up. If you see "rel=nofollow" within the the <a href> html tag, it means that the link is not passing link juice.

Show me some Google love

Always check the directory indexation rate, i.e. roughly how many individual pages within the broader directory website are indexed by Google. Although the technique is not perfect, the easiest and fastest way to check is to head over to Google and type "site:www.example-directory.com" into the search box (replacing www.example-directory.com with the URL of the directory in question). Note that there is no space between the colon and the URL, and the "site" command is typed in all lowercase. Look at how many results Google fetches in response to your search query – is it consistent with the size of the directory? Be extra cautious if you see less than several thousand results.

Link Popularity

It's always helpful to see how well the directory itself is doing in terms of link popularity and trust. To get a snapshot, download and install MozBar, an SEO browser extension (available for Mozilla Firefox and Google Chrome) developed by SEOmoz, a key player in the SEO industry. Navigate to the homepage of the directory in question and fire up the extension. Many of the features require you to sign up as a PRO user (extremely valuable, but also expensive – leave this to your SEO agency), but the information that you are interested in is provided free of charge. We recommend that you pay special attention to the domain mozRank (DmR) and the domain mozTrust (DmT).

DmR measures overall link popularity on a ten-point, logarithmic scale. DmT is also a link popularity metric, but is weighted to reflect the quality of the incoming links – the higher the quality of sites that contain a link pointing to your website, the higher your mozTrust score. DmT is also measured on a ten-point, logarithmic scale.

As a point of reference, the Open Directory Project (ODP), the holy grail of human-edited directories, has a DmR of 7.52, and DmT of 7.64. Yahoo! Directory, also an extremely well-known, link-passing directory, has a DmR of 7.40 and a DmT of 7.54. ODP listing is free, but the review process can take months. It costs $299 to get a listing in the Yahoo! Directory, but the review process is much faster and by all accounts, it's well worth it if you have the cash.

Does this make me look fat?

Finally, don't forget to evaluate the visual layout and design of the directory as a whole. Do you see an overabundance of Google ads? Excessive instances of grammatical mistakes? Does it look like the directory was designed to be a money generator rather than a valuable resource for the web community? All those are giveaways that should make you think twice about spending time filling out a URL submission form.

Some final words

Remember, diversity is good! Just like you wouldn't (or at least shouldn't) put all your money in one company on the stock market, don't rely soley on directories to build your link profile, no matter how SEO-friendly they are. A good SEO knows that the best links are naturally acquired from publishing useful and unique content. Like it or not, the oft repeated phrase "content is king" continues to hold true.

Now it's your turn! What do you look for in a quality, SEO-friendly link directory? Share your thoughts in the comments.

Lukas Pleva is a junior at The University of Chicago. He is currently an account management intern at Webhead Interactive, a full service SEO and online marketing firm in Tampa, Florida.