Google is to launch a free web analytics service that measures the effectiveness of websites and online marketing campaigns.

Google Analytics will allow customers of its AdWords service to see exactly how visitors interact with their website and how their advertising campaigns are faring.

The hosted service will be available in English and 16 other languages, and uses technology from San Diego-based Urchin, which Google acquired in March.

The proposal of a free service is likely to cause ripples in the web analytics business. Urchin's products previously cost £308 a month, which Google reduced to £124 a month.

Website owners will be able to see exactly where visitors come from, which links on the site are getting the most traffic, which pages visitors are viewing, how long people stay on the site, which products on merchant sites are being sold and where people give up in multi-step checkout processes.

Google Analytics will be integrated with AdWords and will offer a new interface within existing AdWords accounts. Marketers can also use the service to track banner, email, non-paid and paid search advertising campaigns from other ad service providers.

Three summary views are available for executives, webmasters and marketing officials.

Julian Smith, online advertising analyst at JupiterResearch, said: "This is good news for Google and for its small to medium advertisers which so far have found it hard to gain good analytics on their advertising campaigns. It will help them become more sophisticated in their approach to online campaigns."

Microsoft includes analytics in its adCenter keyword ad campaign tool, which will compete with Google AdWords. AdCenter is in beta testing in France and Singapore.

Key competitors in the analytics field are WebSideStory, Coremetrics, and Webtrends.