SACRAMENTO, Calif. — In the colorful, centuries-long history of house hunting, when have so many buyers come to the table knowing so much about prices, neighborhoods and school test scores?

Probably never. Credit an average 16 weeks spent browsing the Internet before buyers contact a real estate agent to get serious. Fifteen years into the World Wide Web, home searches once defined by riding around in agents’ sport-utility vehicles — a process in which agents knew all and a buyer knew little — have been thoroughly recast.

Buyers — 84 percent of whom use the Internet for house hunting, according to a California Association of Realtors study — have taken on much of the information gathering formerly done by agents, who occupy the middle of a transaction and typically get a commission of the sales price, half for the seller’s agent and half for the buyer’s agent.

A variety of mostly similar Web sites now enable buyers to browse homes for sale, probe a home’s transaction history, gauge its tax bite, compare area values and even see, via aerial photos, whether the neighbors have planted grass in the backyard.

This maturing of real estate Web sites has raised questions about where agents and brokers fit in and opened some debate about the size of their commissions. At least one online brokerage is trying to redefine the agent pay structure to gain business by making it cheaper to buy and sell.

Still, buyers and agents alike say the sheer complexity of buying and selling homes is keeping the current system largely intact. House buying as a click-here and do-it-yourself job is still much in the realm of fiction.

Today, only about 5 percent of real estate sales occur solely between a buyer and seller, said Glenn Kelman, chief executive officer of Seattle’s Redfin, an online brokerage aiming to simplify home buying.