Google has saved advertisers the hassle of scouring the internet to find the right sites to reach their target audience with its new Ad Planner tool, which it announced on Tuesday.

The tool allows media planners to narrow down their demographics based on gender, age, education and household income. Advertisers input that data, as well as sites associated with the target audience, and Ad Planner will give traffic information and suggest other websites the audience might visit.

The service, which is free, is good news for media planners and publishers, but it could mean bad news for some other companies. Nielson Online and comScore now both find themselves having to compete with Google. Both companies charge to provide similar services, but anticipate that customers will still turn to them for data.

"We haven’t seen, in-depth, the [Google] tool, but the breadth and depth of our data, we feel that clients pay for that,” Susan Hickey, head of marketing for Nielsen Online, told The New York Times.

ComScore, meanwhile, has been trying to stay ahead in the metrics market by expanding into mobile. In a somewhat ironic turn, the company also named Google -- its new competitor -- the No. 1 web property last month.