What is a Cookie? – Part 1

Posted at March 16, 2009

So how do web analytics packages work anyway? Well, that question is a little more complex that it might seem. It depends, are you referring to server based web logs, JavaScript tags? web beacons? or perhaps packet sniffers? These four options comprise the main ways web analytics programs work.

More and more, todays most popular web analytics programs use JavaScript. Examples of systems using JS include Google Analytics, Woopra, Mint, Omniture and more. So – how do they work… and what the heck is a cookie?

When a user visits your website (and you have installed one of these java script code blocks) the web server sends the requested page, along with a snippet of JavaScript code. The page loads and executes the JavaScript which captures all of the wonderful data about your visitor (page views, time on site, browser and so much more). This data is sent back to the collection server (Google, Omniture etc) where it is used to produce the reports for Google Analytics, Omniture Site Catalyst and more.

Some web sites store information about you or your computer in a small file called a cookie. The cookie is stored on your hard drive. Cookies are used when you come back to a web site, the improve load time, remember settings, products added to a cart and a lot more. Sites that run analytics packages like Google Analytics issue first party cookies that allow the site to uniquely, but anonymously, identify individual visitors. This is how a visitors site behaviour is tracked. When a visitor returns to a site, these analytics package are able to remember that the visitor has been to the site before and adjust calculations and analytics metrics accordingly. Rather than registering this user twice as a unique visitor, they are tracked once – for example.

Wikipedia Listing for “Cookies”

Great Google Analytics training video about cookies and how Google Analytics uses them.

There are a few different variations of cookies which I will cover in Part 2.