Seattle online real estate company Redfin is being sued by CoreLogic for patent infringement over its Home Price Tool, a new service that it rolled out in March to help home owners get a better idea of the values of their home.

Publicly-traded and based in Santa Ana, California, CoreLogic is one of the biggest largest providers of advanced property and ownership information. It is also one of the biggest providers of Automated Valuation Models for real estate, helping people obtain appraisals for their homes. The company boasts a market value of $1.8 billion.

At the heart of the suit is U.S. Patent No. 5,361,201, entitled “Real Estate Appraisal Using Predictive Modeling.” CoreLogic alleges that Redfin is infringing on that patent — first assigned in 1994 — with the Home Price Tool.

At the time of its launch two months ago, we asked Redfin how their online service was different from Zillow’s Zestimate. Here’s what Redfin’s Matt Wakefield had to say:

“It’s not an automated valuation model. It’s user-driven, and technology-supported,” explained Wakefield. “Zestimate serves a need in the market for a home owner who is curious about their home’s value, and wants a simple answer. There’s value in it, and that’s why Redfin puts Zestimates on our site. But for people who are serious about selling and want to start the pricing process, they’d be better served creating an estimate on the Home Price Tool and then contacting an agent.”

We’ve reached out to Redfin for additional comment, and we’ll update the post as we hear more.

You can see the full suit — filed in the Eastern District of Texas — here.

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