We've updated the SEOmoz API! Our new Free API gives you Domain Authority, Page Authority, Anchor Texts, mozRank, and also up to 500 links. You can get all your links and metrics with our paid API, the Site Intelligence API. 

With Love,

SEOmoz

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We've been pouring in hours on Linkscape, growing the index (46+ million domains & 36+ billion pages), making the updates closer together and refining the quality of our metrics. Today, we've got two big announcements that should be exciting for nearly everyone in the SEO development and analysis space. First off, we're launching a free Linkscape API to access two of Linkscape's most popular metrics - mozRank of a URL and the number of external links to a URL. Second, we've launched a list of the top 500 sites & pages on the web, ordered by the number of unique root domains linking to them (alongside other interesting SEO metrics).

The Free API

Since Linkscape launched in last October, we've had a lot of feature requests from all kinds of people: big-time agency SEOs, freelance SEOs, tool vendors, friends, and competitors.  One thing that really hit home with us, from all of these people, was the large number of requests for a Linkscape API.  Many of you have been scraping Y!SE, Google, and other data vendors to plug into internal tools and your public widgets for a long time.  We've done our fair share of that kind of work, and we know what a pain it can be.

So to answer that call we are unveiling the completely FREE mozRank API. We've put together a lot of resources to get you started:

1. API Wiki - 99% of the API documentation is here.  It includes a few key pages:
   • Getting started - a good place for newcomers to the API to follow the ordered steps to get going with the service.
   • Generating a valid request - a good breakdown of the request URL you'll send the API.
   • Request/Response - Page detailing request response fields.
   • mozRank API - Page detailing the mozRank API call and response.
2. Google Group - Mailing list for users and developers of the API to ask questions, get help, and communicate with each other.
3. api [at] seomoz [dot] org - You can also email us direct for API questions/help/sales.

So what's in the API and why should you care? First, we're offering mozRank, our logarithmic scale metric of global link popularity based on the importance of links pointing to a page. It's similar in intuition to the algorithms powering Google's PageRank, Yahoo!'s WebRank & Microsoft's StaticRank. Second, we provide a raw count of external, juice-passing links. This number indicates how many links we've seen across the web pointing to a given page from external sites, excluding no-followed links.

We chose those metrics to share thanks in part the results of correlation testing we've been doing for a long time (this research should launch on the blog later this week). We've traditionally looked at metrics like Google Toolbar PageRank for SEO and internet marketing purposes. The consensus we've heard is that this metric isn't great for predicting rankings, but it's all we've got. We're hoping to change that.

Our results show that this instinct about Toolbar PageRank can be statistically supported. It's not completely wrong, but I think you'll agree that this metric is probably not designed for some of the marketing purposes to which we are putting it.  In particular we've found that as Toolbar PageRank ages, it drifts out of correlation with rankings. With updates coming as infrequently as six months to a year, this effect can be substantial. Toolbar PageRank also seems to be correlated with a variety of effects, from link popularity, to domain authority, to penalties and trust. This makes many uses quite difficult: did your Toolbar PageRank drop because you lost some important links? Or were you caught with paid links? Is the new juice you seem to have because of that linkbait post you wrote, or because your domain has achieved the next level of global authority in general?

We believe that mozRank is a much better metric for these marketing and optimization purposes (and is often exceptionally valuable when compared up against Toolbar PageRank). We are committed to keeping mozRank as updated as we possibly can: so far we've updated mozRank twice, with one to two months between updates. We're actively working to make the updates closer to one month apart. MozRank is also measuring a single effect: link popularity. Coupled with the count of external links (also included in the free API), you can get a fair measurement of two of the most important ranking dimensions. We're going to continue measuring the other effects I mentioned (domain authority in domain mozRank and trust in mozTrust), along with many other factors in our web-based Linkscape tool.

BTW - You can already see the mozRank API in action with Quirk's SearchStatus toolbar:

Along with the SEOmoz Toolbar (which shows a lot of additional metrics for PRO members), this is one of only two toolbars that currently show mozRank & external link counts.

The Top 500 Most Linked-To Domains & Pages on the Web

We've also compiled a list of the most linked-to sites & pages on the web, according to our index. We found this data fascinating - seeing which domains and URLs had amassed incredibly high numbers of links, looking at the stats surrounding them and parsing the cause for their meteoric link counts. We also made some excellent discoveries about spam filtering, the value of our metrics and the power of having a plug-in or embedded widget that links back (just look at how many of the top linked-to pages & domains are popular as a result of this phenomenon).

Since the chart mostly speaks for itself, I'll hold off on a thorough analysis, but needless to say, there are a great number of interesting observations and hypotheses to be drawn from the list. And, while it's awesome to look at and play with now (there's a downloadable CSV as well), it's going to get even more exciting as we update the rises and falls as Linkscape updates and the web progresses. Just as an example, if we had run this on our first index in October of 2008, I doubt we'd see Twitter near the top. Today, it's in position #69, and I'm guessing it's trending upwards in the next crawl.

We hope you enjoy both of these new features around Linkscape. Spread them around and report your findings and applications.