Social media analytics firm PostRank has released two Application Programming Interfaces (APIs) that will alow developers to track reader engagement in any group of blogs or around any single link with just 15 seconds of latency. Technorati's announcement last week that it is scaling back and changing its blog ranking activities, and putting new emphasis on in its blog advertising network, prompted PostRank to launch their APIs now.
The same API used for ranking by the AdAge 150 and the Atlantic Monthly's new political blogger leaderboard is thus now generally available. Determining the most-closely watched bloggers on niche topics is something a lot of people want to do for a wide variety of reasons - when that determination can be made programatically you can jump into the center of a conversation quickly.
PostRank looks at any RSS feed it's given and scores all the items in those feeds for number of comments left, inbound links, times bookmarked in Delicious, being shared on Twitter and several related metrics. The company says it has agreements with many services to have data pushed to them and queries the Delicious endpoint themselves every 1 second, for example.
Some good sample lists are Postrank CTO Ilya Grigorik's favorite a href="http://www.postrank.com/user/igrigorik/topic/cloud">cloud computing blogs or the general list of top design blogs. The new APIs will make it easy to build lists around any topic or group and display that data on other sites.

Blogsearch data has been a consistent problem for PostRank, both Technorati and Google Blogsearch data has been inconsistent for the company. PostRank says it will be launching its own trackback discovery service shortly.
While some meme-tracking services struggle with niches where blogs don't heavily link to eachother, PostRank says that by tracking multiple forms of user interaction it has captured data that closely resembles what can be found from services tracking absolute web traffic to individual sites.
Last month PostRank released a new analytics tool that displays social media engagement on top of Google Analytics data. The new APIs will allow 1000 requests a day for free for noncommercial use, commercial licenses are available as well.

Disclosure: PostRank is a sponsor of the forthcoming ReadWrite Real-Time Web Summit. It's also one of our favorite services on the web.
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I tried Technorati's advertising network a while back in beta mode. Wasn't overly enthused. It uses AdEngages script to host it. They had all sorts of errors going on. I even got a thank you for your order from AdEngage on one order.
It just seems like Technorati does many things this way, half a$$. All PostRank has to do is keep it tight, and they should quickly rank as the new champ here.
Hi Marshall:
There is also the List of Change bloggers which uses the same code of the ad age bloggers list
http://www.livingstonbuzz.com/listofchange/
It indexes nonprofit blogs.
Marshall, I think you may have misconstrued some of what was written by VentureBeat. First, Technorati is hardly "faltering" -- actually quite the opposite. Second, "scaling back" also wouldn't be accurate unless you think cleaning up the web's largest blog index and directory to produce better results and a much more relevant Authority Rank is "scaling back". No doubt, it looks like PostRank is doing something pretty cool and useful, and it'd be better to focus solely on the great utility they offer. However, it's premature to judge what Technorati is launching in the near future, and it is not remotely accurate to characterize the company in a doubtful light.