Zillow.com said it will offer its application programming interface for free to third-party realty web sites as the eight-month-old online firm continues to carve out a complementary role as the default research site in the real estate business.

Despite its rapid rise as one of the most popular real estate research sites in the United States, Zillow continues to be careful about the industry’s data sensitivities, by building its own extensive database without piggybacking on the industry’s proprietary data.

Now Seattle-based Zillow, which was started by Expedia founder Rich Barton, said Thursday it is opening up its database of 68 million U.S. homes to local agent sites and mini real estate portals.

Through its available APIs, Zillow is offering third parties access to its property details and home valuations.

The company’s home valuations include market trend information, comparable sales data, valuation charts, and Zestimates, Zillow’s proprietary computation of home values.

The property detail API includes detailed information about specific homes, including physical data such as the number of rooms, bedrooms, etc., information about the historical sale price of the houses, along with the tax assessment.

Open to Consumers

Last month Zillow announced it was opening up its database to homeowners so they could add missing information to the existing description of their homes (see Zillow Opens Up, Wiki Style).

Homeowners can also recalculate the valuation of their homes online. The homeowner’s valuation will be published in the database alongside Zillow’s preexisting valuation.

Opening up the database to homeowner updates is Zillow’s attempt to end-run a structural flaw in the online home data business—no feet on the street.

Local realtors can eyeball properties from time to time and update the record for changes such as the addition of a garage or the installation of an in-ground pool. Online real estate sites don’t usually have a local presence.

Zillow said it has already launched more than 30 implementations of its API with companies such as Redfin, ZipRealty, Yahoo Real Estate, and Prudential Northern California and Nevada. The company said it has also licensed its APIs to a number of smaller organizations.

There are a number of conditions attached to the use of Zillow’s data. For instance, the data must be used on a transactional basis and not accessed in bulk.

Registered users are limited to 1,000 calls to the Home Valuations API and the Property Details API per day. The company requires users with more traffic to pass an audit and review examination.

Contact the writer:CMedford@RedHerring.com

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