James Mowery of TechInDemand.com got in touch with me a few weeks ago and wondered which plugin sites like Engadget and Autoblogs were using that allowed for comment rating. I digged into the source code for those websites and couldn’t figure it out. Today, I have finally discovered which plugin those guys are using and figured I would share it here.

Its called, Comment Karma. Comment Karma is a plugin you can use to allow your visitors to rate each others comments. Like Digg, you can click a thumbs up or thumbs down icon which will give that comment either a positive or negative number.

This plugin was created in 2006 so I’m not sure how it will work with WordPress 2.3 but it’s worth a shot. One thing worth noting is that, the rating cache is set to 120 seconds.

If you’re using WP-Cache or similar the icons will not show up gray, nor will the numbers be updated if you reload the page until the page expires. However if a user votes again it will throw them an error. I’ve worked around this by setting the cache for 120 seconds. That way the server doesn’t get hammered with SQL queries, but you still see the comments being moderated in almost real time.

There is a similar service in SezWho, but by using this plugin, you can keep the comment ratings local to your WordPress install which may improve loading times for your site. I may install this plugin in place of SezWho just for that reason alone. If you’re interested in using this plugin, check out the official Comment Karma plugin page for directions on how to install it into your blog.