Real estate technology is in the middle of its largest transformation in decades.

MLS and developers are racing to transition away from RETS before the December 2018 deadline.

Long considered the gold standard for IDX, the framework is now all but obsolete.

The Real Estate Standards Organization has announced RETS will be retired in June.

The replacement?


It’s a faster, more flexible data standard that RESO promises will push real estate deeper in to mobile and social applications.

In this moment of transition its important to remember where we are going and from where we came.

So we put together RESO Web API v. RETS to highlight the differences and commonalities between the two standards.

Let’s start in the past.


The Real Estate Transaction Standard (RETS) was created in 1999,  by the National Association of Realtors. As one of the largest standardizations efforts in history, RETS was a major force in shaping the industry we know today.

For the first time under RETS, MLS and technology partners could transfer property listing data with a level of predictability.

This was a massive step toward addressing decentralization problems among the nation’s 700+ MLS.


RETS provided a framework for property listing data transfers.

It allowed IDX software to query an MLS database and synchronize updates.

These queries provided the same results across MLS (with some minor differences).

This streamlining spawned dozens of real estate technology companies, like Realtyna, who now could serve clients around the country with minimal coding.

It also meant agents and brokers could display properties from multiple MLS,  on the same website without too much trouble.


RETS included a number of tradeoffs. Based on XML, the framework required anyone with a feed to download the entire listing database to their local servers and then to run updates progressively.

Many MLS contain 100 GBs or more of listing data. To handle all of this data, agents and brokers, had to have large and expensive hosting plans.

Further, with copies of their listing data scattered across the web, the MLS never could be sure of security.


So in 2016, RESO started rolling out RESO Web API.

Like RETS, RESO Web API is designed to conform real estate technology practices in the absence of a nationwide MLS.

Unlike RETS, RESO Web API greatly streamlines the transfer process.


As an API (application programming interface), the new RESO standard allows IDX software to call MLS directly.

It’s hard to underestimate the impact of this change.

Imagine a user that runs a property search on an IDX website. Under RETS that search would query a database on the IDX site’s servers and return results.

Under RESO Web API, the search queries and returns results directly from the MLS servers.

This eliminates the need for large local hosting purchases and reduces security concerns from the MLS.

But that’s not the only benefit of RESO Web API.

The new standard is also based on OData, a global technology protocol. This gives developers a familiar platform to build, software, applications, and plugins.

RESO says these innovations will save agents and accelerate the development of new real estate technology products.


Because of these advantages, RESO considers the Web API to be the superior standard.

It says RESO Web API, “makes everyone’s life simpler.”

So MLS and real estate technology companies, including Realtyna, are racing to make the switch.

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The opinions or information expressed in this article are those of the author and do not necessarily reflect the official views, policy, or position of Realtyna. The information on Realtyna’s Website is general, for informational purposes only, and is not to be relied upon or interpreted as real estate, legal, accounting, or other professional advice or a substitute. Please discuss anything related to the certification process, professional advice or legal procedures with your MLS providers.

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  • Richard Stark
    Posted at 08:54h, 07 October

    In reality, all they did was trade one protocol for the other. You still have to download a full set of listings, then incrementally query the MLS server for changes. OData is an improvement, but most queries are simple anyway. It has been an expensive ride to transition and you can guarantee, someone on an advisory committee somewhere is benefiting financially by the decision.

    • Tait Militana
      Posted at 05:05h, 08 October

      Thanks for your comment, Richard. You’re right that replicating data locally still requires a database download. But the change also helps developers and agents get their sites online faster.