Today, Google launched a new project called Sidewiki, which is a browser sidebar that lets users add footnotes to any existing Web page, even if the main site doesn't allow comments. Sidewiki has been added as a feature on Google Toolbar for Firefox and Internet Explorer, and the team today said they're working on an edition for Chrome, too.

Sidewiki appears as a field on the left hand side of the browser, where users can post contextual commentary. If it's a site paraphrasing a piece of literature and a user happens to have a link to the full text, it can be added there. While it can very easily suffer from "FIRST!" syndrome or serve as a spam advertisement platform, posts are not anonymous. And as Sundar Pichai, VP of Google Product Management and Michal Cierniak, Engineering Lead for Google Sidewiki today said the content will be ranked by quality.

"In developing Sidewiki, we wanted to make sure that you'll see the most relevant entries first. We worked hard from the beginning to figure out which ones should appear on top and how to best order them. So instead of displaying the most recent entries first, we rank Sidewiki entries using an algorithm that promotes the most useful, high-quality entries. It takes into account feedback from you and other users, previous entries made by the same author and many other signals we developed," Pichai and Cierniak wrote in Google's official blog today.

The API for Sidewiki is available in Google Code Labs.