Alexa Internet, Inc. is a California-based subsidiary company of Amazon.com that is best known for operating a website that provides information on web traffic to other websites.

Operations and history

Alexa Internet was founded in 1996 by Brewster Kahle and Bruce Gilliat. The company offered a toolbar that gave Internet users guidance on where to go next, based on the traffic patterns of its user community. Alexa also offered context for each site visited: to whom it was registered, how many pages it had, how many other sites pointed to it, and how frequently it was updated. Engineers at Alexa, in cooperation with the Internet Archive, created the Internet Archive's Wayback Machine. Alexa also supplies the Internet Archive with web crawls.

In 1999, Alexa was acquired by Amazon.com for about $250 million in Amazon stock.

The company's premises are in Building 37 of the Presidio of San Francisco.

Alexa began a partnership with Google in spring 2002, and with the Open Directory Project in January 2003. Live Search replaced Google as a provider of search results in May 2006. In September 2006, they began using their own Search Platform to serve results. In December 2006, they released Alexa Image Search. Built in-house, it is the first major application to be built on their Web Platform.

Alexa also provides "site info" for the A9.com search engine.

In December 2005, Alexa opened its extensive search index and web-crawling amenities to third party programs through a comprehensive set of web services and APIs. These could be used, for instance, to construct vertical search engines that could run on Alexa's own servers or elsewhere. Uniquely, their Web Search Platform gives developers access to their raw crawl data. In May 2007, Alexa changed their API to require comparisons be limited to 3 sites, reduced size embedded graphs be shown using Flash, and mandatory embedded BritePic ads.

In April 2007, Alexa v. Hornbaker was filed to stop trademark infringement by the statsaholic service. In the lawsuit, Alexa alleges that Hornbaker is stealing traffic graphs for profit, and that the primary purpose of his site is to display graphs that are generated by Alexa's servers. Hornbaker removed the term Alexa from his service name on March 19, 2007.

Concerns over Alexa rank information and the Alexa Toolbar

Alexa ranks sites based on visits from users of its Alexa Toolbar for Internet Explorer and from integrated sidebars in Mozilla and Netscape. In addition to their own statusbar extension, Sparky (released July 2007), there are several third-party extensions for Mozilla Firefox:

SearchStatus shows Google PageRank and Alexa TrafficRank

About This Site Firefox plug-in that shows metadata from Alexa TrafficRank.

There is some controversy over how representative Alexa's user base is of typical Internet behavior. If Alexa's user base is a fair statistical sample of the Internet user population (e.g., a random sample of sufficient size), Alexa's ranking should be quite accurate. In reality, not much is known about the sample and possible sampling biases. Alexa itself notes several examples. A known source of bias is the self-selecting, opt-in nature of Alexa traffic tracking software installation, but the significance of this bias on rankings is not reported.