SAN FRANCISCO - Hoping to leave an even bigger imprint on the Internet, Google Inc. is opening up its vast online index so other Web sites can build their own specialty search engines.
The free service, unveiled late Monday, marks Google's latest attempt to expand its lucrative online advertising network and extend its influence on how people navigate the Internet.
"Now people can get the power of Google search even when they're not on Google.com," said Shashi Seth, group product manager for the custom search engine.
Mountain View-based Google already dominates Internet search, with a 45 percent share of the U.S. market through September, according to comScore Media Metrix.
The custom tools will allow other Web sites to limit the range of material that they want to include in their search indexes as well as rank the importance of specific pages.
The concept mirrors the approach of a small startup called Rollyo.com.
Google said it simplified the process so even technological neophytes should be able to tailor their own search engines in 10 minutes or so.
Hundreds of Web sites already rely on Google's search technology, but most of those arrangements either focus exclusively on content posted within a partner's site or span the billions of pages indexed in Google's complete database.
Google designed its customizing system to appeal to Web sites that want their search engines to focus on specific topics. For instance, a fishing site might tailor Google's customized search engine so it doesn't scan music sites to minimize the chances for confusion when the term "bass" is entered.
Software maker Intuit Inc. already has used Google's customized tools to create a specialty search engine for a new Web site, JumpUp.com, devoted to small business issues.
In return for providing a tailor-made search index, Google will display short, text-based ads tied to the search requests entered at participating Web sites.
The revenue generated from those ads will be shared with the Web site owners - the same approach that has enabled Google to build the Internet's biggest advertising network and establish itself among the world's most valuable companies with a market value of nearly $150 billion after just eight years in business.
Web sites run by government agencies, universities and nonprofit groups will be permitted to deploy the custom search tools without being forced to run Google's ads.