What Technology Stack Do Zillow, Redfin and Realtor.com Use for Property Listings?

Recently, we published an article about the current state of the online real estate market and developing a Zillow-like real estate marketplace. This time, we’ll reveal the technology stacks that Zillow, Redfin, and Realtor.com are using. This will help you figure out how things really work underneath the beautiful interfaces of real estate apps and websites. So let’s dive into real estate app development and find out where real estate platforms take data from.

What’s the difference between Zillow, Realtor.com, and Redfin?

From the great variety of real estate platforms on the market, Zillow, Redfin, and Realtor.com can be named the real estate traffic leaders.

According to Statista, Zillow is the leading real estate app in the US, with 36 million visits a month as of May 2018. Trulia, owned by Zillow,  is the second most popular real estate website, with 23 million monthly visits. Yahoo! Homes, with 20 million visitors, and Realtor.com, with 18 million visitors, are next on the list. Redfin closes the top five with 6 million visitors. Let’s compare these platforms.

How they started 

Zillow is a real estate company that was founded in 2006 by Rich Barton and Lloyd Frink, former Microsoft executives and founders of the leading travel website Expedia. Zillow started in Seattle as a real estate marketplace targeting buyers and sellers. It attracted users by providing convenient tools for both target groups. First, Zillow offered publicly available market data, free listings for owners, and Zestimates — free and unbiased home value estimates based on publicly available and user-submitted data. With time, it added features such as Zillow Advice, a mortgage calculator, an agent finder, and Zillow Home Design. 



As the platform grew, it started to acquire real estate companies. In 2013, Zillow spent $50 million to buy StreetEasy, an apartment rental market. The next year it acquired HotPads, a map-based real estate marketplace. It also acquired Retsly to help developers access real estate data from multiple listing services (MLSs). In 2015, Zillow acquired one of its largest competitors, Trulia, for $3.5 billion. 

Redfin was created in 2004 by David Eraker, Michael Dougherty, and David Selinger. The company was a pioneer of map-based real estate search even before Google Maps appeared. Redfin started as a local company operating in San Diego. It grew fast in San Diego and then expanded to more than 80 markets all across the US. Redfin was the first real estate company to add for-sale-by-owner listings, combining listings from multiple listing services with homes listed by owners.

Realtor.com is the oldest company on this list, founded back in 1995 in the San Francisco Bay Area. It’s considered the grandfather of the whole online real estate industry. Realtor.com is the official site of the National Association of Realtors® and is operated by Move, Inc., a subsidiary of News Corp, which belongs to Rupert Murdoch. The company started as a closed network for members of the National Association of Realtors and relaunched a year later as a public website with property listings. 


[The Realtor.com app]

Business models

Zillow and Realtor.com are real estate aggregators that get revenue from advertisements. 

Zillow offers several advertising options:

  • Zillow sells advertisements to mortgage lenders, property management companies, general contractors, home organization retailers, and other businesses. Zillow charges them based on cost per click or cost per thousand impressions.

  • Zillow also has a premier agent program. A premier agent pays Zillow a monthly fee starting from $10 to appear on all the property listings on the site. Real estate agents also pay Zillow based on the number of ad impressions delivered to users in a specified area. 

Unlike Zillow and Realtor.com, Redfin is an actual brokerage that pays its real estate agents a base salary and makes money when users buy or sell homes through its agents. The company has a seller’s listing fee that depends on the location of the house. For instance, in Atlanta the fee is 1.5 percent, while in Denver it’s 1 percent.


[The Redfin app]

Relevance of data

Listings on Realtor.com and Redfin are supposed to be accurate and up-to-date because these websites are directly linked to MLSs. According to a study by Redfin titled Dedication to Data Quality, MLS feeds appear on Redfin and Realtor.com as soon as they’re listed by an agent and get updated every 10 minutes. It may take 48 hours for a for-sale-by-owner (FSBO) listing to appear on Redfin since Redfin carefully check listings published by owners.

Zillow claims that it takes from 24 to 48 hours for MLS listings to appear on the site. FSBO listings must be posted manually on Zillow through a homeowner’s profile. Every FSBO listing goes through a verification process, so it takes up to 72 hours for them to appear on the website.

Listings on Realtor.com are loaded into the website’s database within one to five business days. The company works closely with every MLS in the country to decrease the wait time. 

Where do Zillow, Realtor.com, and Redfin get their data from?

Multiple listing services

Real estate data in the US comes from two main sources: individual real estate agents and real estate brokers who are members of local associations of realtors and who enter information in the MLSs that realtors associations publish for their local communities.

The good thing is that MLSs allow real estate portals like Zillow, Redfin, and Realtor.com to publish MLS listings on their websites.

The bad thing is that MLSs are quite hard to access. There’s no public API you can use to just pull the data from, and they restrict membership and access to real estate brokers and their agents, which means that a person selling their own property can’t put a listing directly into an MLS.

It’s important to note that public property details should comply with certain rules established by the National Association of Realtors (NAR) and followed by IDX (Internet Data Exchange).

MLSs also exist in some European countries including the Czech Republic, Italy, and the UK. In Germany, there are three listing services: Immobilienscout 24 and Immowelt.

So if there’s no public API, what sources can real estate aggregator companies use to get property listings?

  • Agents and brokers

Zillow is doing fine attracting real estate agents and brokers to their website. The main way the company attracts agents is by providing them with a convenient tool to manage all their listings in one place.

The Draw the Area To Search feature

[Redfin has a convenient Draw the Area To Search feature]

  • Local MLSs

Trulia and Zillow get access to local MLSs by negotiating data sharing and syndication agreements. Redfin, on the other hand, doesn’t have any of that headache. As a brokerage, it’s free to use data from its membership in the Realtors MLS.

In this regard, it seems like Zillow is doing things the hard way. After all, it could become a brokerage and pull data directly from an MLS. However, becoming a brokerage imposes a lot of legal obligations on a company because then they need to participate in sales by representing buyers and sellers within their MLS, which basically means they have to employ agents and manage them across the whole country.

  • Listing syndication platforms

Because there are hundreds of MLSs all over the US, it’s extremely burdensome to negotiate agreements with all of them, especially if you operate nationwide. That’s why the largest aggregator websites enter into data sharing agreements with national real estate companies to get their data directly.
These companies include 365 Connect (a provider of technology for the housing industry), the RealBird social media and mobile listing marketing platform, and JBGoodwin Realtors. ListHub is one of the largest aggregators of real estate listing data in the US. 

You would need to do three things to get access to those platforms: get licensed in every state, join an MLS, and integrate data that doesn’t follow a consistent standard across the 900+ MLSs. 

For Sale by Owner and Make Me Move listings

Zillow also allows For Sale By Owner listings, allowing homeowners to list their own homes without the assistance of professional agents. Homeowners can post listings directly on the platform after registering. Listings are verified, and if they don’t violate Zillow’s rules, they’re posted within 72 hours. 

FSBO listings on Zillow

[FSBO listings on Zillow]

Redfin takes information from forsalebyowner.com, Fizber.com, and FSBO.com and doesn’t allow users to post FSBO listings directly on their website. But its primary data source is MLSs, so in case someone is trying to post a listing on an MLS and as an FSBO, the website will display only the MLS listing. 
Realtor.com is sceptical about FSBO listings, so it doesn’t allow homeowners to post them on the platform. 

What’s interesting, however, is that properties on Zillow don’t necessarily have a “for sale” label. The owner of a property can state the price they'd be willing to sell their home for without actually putting it on the market. This type of listing is called Make Me Move. It’s a great way to measure interest from potential buyers and even get the right offers sooner. Potentially, FSBO is a great opportunity for emerging real estate businesses in the US.

How can I access real estate databases?

The biggest problem with MLS listings isn’t even the license. It’s the different database implementations across MLSs. To enable data exchange between an MLS database and your website, you need to implement IDX (Internet Data Exchange). There are a couple of ways to do that.

You can use RETS (the Real Estate Transaction Standard), a framework used to give brokers, agents, and third parties access to listing and transaction data. RETS allows you to download listings in manageable segments, and only those that have been recently added or changed will need to be updated. RETS is XML-based, and there’s a wide variety of open source tools and libraries for working with RETS data. However, these tools still aren’t perfect.

Another solution is to use the RESO Web API, a standard introduced in 2016. It streamlines the movement of listings and can significantly cut local hosting and security costs. Paired with the RESO Data Dictionary, the web API also standardizes the structure of property listings.

There are also third-party services that provide APIs that normalize data flows from MLSs. You can check out iHomeFinder, Spark, SimplyRets, and the Optima Express IDX Plugin for WordPress sites.

An important step in real estate platform development is choosing the technology stack. You need to build a robust backend to be able to manage your data properly. Redfin’s main development languages are Java and Python. They use a PostgreSQL database on the backend. They also use the IntelliJ IDEA integrated development environment, Git for version control, Jenkins for continuous integration, and JIRA for project management. React Native is used for cross-platform mobile development. 

Zillow’s main programming languages are Python and Java. They use Amazon EC2 for cloud hosting and Amazon S3 for cloud storage. Zillow uses the Git version control system and Jenkins for continuous integration. They also use Realm and CoreData to manage big sets of data and use Swift and Java for mobile app development. 

What other data does a real estate app need?

Other than information about properties, a real estate app or website generally has data about neighborhoods, schools, points of interest, demographics, past sales, and other information that improves the home buying and selling experience.


[Realtor.com shows schools and police departments nearby]

Zillow provides APIs with neighborhood information for their listings and a dataset that contains neighborhood boundaries. Here are other important APIs to retrieve geographical and neighborhood information:

  • GeoNames has a comprehensive dataset of over 10 million geographical names.

  • The Google Places API gives you information about nearby places such as cafes, cinemas, and sports clubs. 

  • MapBox allows you to build custom maps for real estate listings. Read about why StreetEasy, one of Zillow’s companies, switched from Google to MapBox.

  • Almost all cities in the US have open data portals with a variety of information that you can use in your app. For example, you can find open data sets for New York City, Chicago, and Los Angeles.

Real estate app development is challenging! But now you know what makes it possible for huge companies like Zillow, Redfin, and Realtor.com to pull real estate data into their apps and websites. 

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