Alexa is a free tool offered by Amazon inc., that helps to assess the traffic of any website. It can be used to compare several websites in the same field and to detect traffic variations for a given website. But Alexa rankings are biased by the fact that rankings are based on traffic from Alexa toolbar users only. Alexa offers many rankings according to topic, countries and languages, but the sample of Alexa users is not large enough to give accuracy to sites ranked above, say, the 10,000th global position. Also, Alexa users are numerous among the marketing & SEO world and thus such websites have much better rankings that they should. As a good Alexa ranking can help seducing advertisers, there are also paid services that make you climb artificially in Alexa.

Alexa rankings are displayed in Alexa.com or in toolbars, which can be downloaded for free. The Alexa toolbar, which offers also other services such as Google search, is one of them. The Alexa toolbar is available for IE and for Firefox (under the name of Sparky), but not for Macintosh. English is the only language supported until now. The Alexa toolbar is seen by most antivirus as a spyware, because it sends to Alexa.com information about web users navigation.