StumbleUpon is a web browser plugin that allows its users to discover and rate webpages, photos, videos, and news articles. These webpages are typically presented when the user — known within the community as a Stumbler — clicks the “Stumble!” button on the browser's toolbar. StumbleUpon chooses which new webpage to display based on the user's ratings of previous pages, ratings by his/her friends, and by the ratings of users with similar interests. i.e. it is a recommendation system which uses peer and social networking principles. There is also one-click blogging built in as well. Users can rate, or choose not to rate, any webpage with a thumbs up or thumbs down, and clicking the Stumble button resembles “channel-surfing” the web. Toolbar versions exist for Firefox, Mozilla Application Suite and Internet Explorer.
StumbleUpon uses collaborative filtering (an automated process combining human opinions with machine learning of personal preference) to create virtual communities of like-minded websurfers. Rating websites updates a personal profile (a blog-style record of rated sites) and generates peer networks of websurfers linked by common interest. These social networks coordinate the distribution of web content, such that users ‘stumble upon' pages explicitly recommended by friends and peers.
Users rate a site by giving it a thumbs up, thumbs down or neutral (neither thumbs up or down) selection on the StumbleUpon toolbar, and can optionally leave additional commentary for the site's review page, which also appears on the user's blog. This social content discovery approach automates the “word-of-mouth” referral of peer-approved websites and simplifies web navigation.
Stumblers also have the ability to rate and review each others' blogs as well as join interest groups, which are community forums for specific topics. Users can post comments much like a discussion board in these groups and post websites that apply to the specific topic
On December 13, 2006, StumbleUpon launched their StumbleVideo site at http://video.stumbleupon.com/. The new site allows users without a toolbar to “stumble” through all the videos that toolbar users have submitted and rate them using an AJAX interface. The site currently aggregates videos from YouTube, Google Video, Metacafe, and MySpace Videos.
StumbleUpon launched a version of StumbleVideo for the Opera browser that runs on the Wii console on February 12, 2007. This version of StumbleVideo is optimized for the Wii's smaller screen resolution and offers similar functionality to that of the original version.