The present and future of real estate data standards

Mark Lesswing


Standardizing data in the real estate industry has been a joint effort of practitioners, service providers and vendors for over two decades. The Real Estate Standards Organization (RESO), which became a nonprofit trade organization in 2011, has played a key role in the effort since NAR founded it in 2000.  

When NAR spun RESO off in 2011 as an industrywide initiative, membership grew quickly to hundreds of vendors, MLS organizations and brokerages. There are two main parts to the RESO effort: what data is being transmitted, which is covered by the Data Dictionary, and how data gets moved from point to point, which is covered by the RESO Web API. 

Elected by members, RESO leadership direct efforts to create standards, foster adoption and certify implementations of the RESO standards. I currently sit on the RESO board of directors and have an inside view on where it is and where it and real estate data standards are headed.

As RESO plays a key role in helping push the industry data and technology forward, this article highlights where it is in its effort to provide and implement data standards across the industry, including what is has done and is working on now.

Standardized Fields

Before standardization there were several methods that could be used for downloading MLS information. The methods included both transport and data components. One of the most popular approaches featured an FTP access as a transport that was used to obtain a data file. The file was either positionally arranged or tagged with field names that were unique to the MLS.

With the development of the Data Dictionary, in which over 800 MLS data fields are defined and standardized, brokerages gained the ability to streamline their digital advertising on portals and other listing sites. On the flipside, tech vendors, with clients in multiple MLSs, could more efficiently build, operate and innovate products.

In addition, the standardization of property terms across MLSs has lowered the cost for MLSs to switch MLS system providers as they choose. Without data standardization, the costs to setup a system with a new provider would be much higher and the work required more involved. More terms continually get added to the dictionary and it gets periodic updates, the current version is version 1.7.

Some of the data types now standardized include:

  • Property data relating to the listing and the property itself such as listing price, year built, zoning, window features, showing days, etc.

  • Member data including, name, MLS ID, license number, job title, last login timestamp, Realtor association identification

  • Office information including, franchise affiliation, office ID, office contact information, etc.

  • Various other categories of data such as open house information, showing information, transaction history and internet tracking

The RESO Data Dictionary has been an important time reducer for software developers because they can count on the same names in every MLS and focus their limited resources on improved capabilities such as user interfaces, mobile apps or analytics. 

Standardized, Modern Web API

RESO also has developed the RESO Web API protocol, which better supports mobile applications and enables the tech vendors and the industry at large to develop deeper future cross-industry integrations with industries adjacent to residential real estate, including mortgage, title and insurance.

While the RESO Web API is up and functional, multiple MLSs, vendors and MLS system providers still use the previous protocol, Real Estate Transaction Standard (RETS), which complicates the industry data landscape, as data-handling across geographies and vendors is inconsistent. One of the key limitations of RETS is that it is unique to real estate; no other industry uses the protocol to transport data, which requires developers not familiar with the industry to learn a new technical language before jumping in. This limits real estate’s technology talent pool and makes it more expensive.

Until the industry moves completely to the RESO Web API, brokers, MLSs and tech vendors will not realize the full promise of modern technology.

RESO certifies the MLSs and tech vendors on its latest protocols, and notes those who are not up to date.

RESO also developed some data identifiers, including the Universal Property Identifier, which provides an industrywide standard for the way to identify properties. This ensures that data about a property, regardless of the various hands it passes through remains coherent, and does not accidentally end up treating one property as two or more. RESO has adopted this now and it helps prevent confusion of property data as it passes through multiple systems.

The future

Even as the industry moves to fully adopt the RESO Web API, a new type of data transport protocol lurks on the horizon that could add enhanced functionality. It lies, perhaps not surprisingly, likely with blockchain technology and the Web3 movement.

One of the key features of this potential new protocol include tying business rules to data fields. This would ensure that required data fields are filled out and also entered in the specified format. The current protocol does not allow for this, and this smart-contract feature, is a key one of blockchain technology. The industry is likely years out from this protocol, but data experts are beginning to discuss features like these in what will come next.

In addition, RESO is currently working on two additional types of real estate data identifiers: the Unique Organization Identifier (UOI) and the Unique Licensee Identifier (ULI).

The UOI will tie the source of real estate data to the data itself, so as it moves through different systems and users, the data publisher will always be clearly identified. This protocol, likely approximately two years from completion, will better allow for publishers to get credit, whether by payment or attribution, for the real estate data they create.

The ULI represents an ambitious aim to create real estate data standards that apply across all facets of the real estate ecosystem including title, insurance, mortgage and even commercial. By creating cross-industry real estate data standards with the ULI, the long-held dream of an all-in-one transaction platform will cross one key hurdle to realization. While a RESO work group is actively working on this, the protocol may take five or more years to develop.


Real estate data standards play a crucial role in the advancement of industrywide technology. If you want to see technology improve, learn more about RESO, and get involved. I’d be happy to answer any questions you may have at