Zillow opens up real estate APIs

Zillow Inc. has decided to let other Web sites tap into its repository of residential real estate for free, in an attempt to reach new users.

The company made available on Thursday two application programming interfaces (APIs) to external developers so they can incorporate into their Web sites Zillow’s property valuation and home details.

Previously, Zillow had provided access to its services and data on a case-by-case basis to those that requested it, such as Yahoo Inc., which uses the Zillow data in its real estate section. However, Zillow has now decided to make the APIs available to anyone for free, as long as they comply with its terms of service, which stipulate including certain links to its Web site.

The company foresees the APIs being interesting to real estate brokerages, individual agents, mortgage lenders and others in this field.

Zillow’s move to open up its services and data to other Web sites fits into a trend among providers of Internet services, such as Google Inc. and Yahoo. By letting third-party Web sites provide their services and data, these companies multiply their presence on the Web and gain users. Meanwhile, the third-party Web sites are able to offer services they lack, in theory becoming more attractive to users.

Zillow’s “home valuation” API provides value estimates, charts and comparable properties, while the “property details” API includes historical sales, taxes and structure information, such as a home’s size and number of bedrooms.

Zillow, which is privately held and has about 125 employees, launched its site in February of this year and has data on about 68 million U.S. residential properties. It gets the raw data from public sources and then grinds it through a proprietary analysis system to generate value estimates.

About 3.4 million unique visitors came to the site in September, a company spokeswoman said. It generates revenue from advertising.

More information about the API program is available at the company’s Web site.