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RCF is the result of a desire for a normative JSON data format that corresponds with the RESO Data Dictionary and is compatible with existing Web API implementations for retrieving or creating data. | VIEW THE RCF SPECIFICATION

The RESO Web API is primarily used by MLS data providers, but other participants in the real estate transaction and ecosystem benefit from having a standard payload format to provide interoperability between various systems. RCF fulfills this need for the likes of tour, assessment, and showing providers or photographers, as Data Dictionary JSON format is not limited to Web APIs and may be used with any data source.


RESO uses sophisticated certification software to ensure that technology systems conform to ratified standards. Certification proves to others that your technology system speaks a common standards language. From Web API to Data Dictionary to RESO Common Format and more, technology companies can achieve a RESO stamp of approval through certification. Certification testing questions may be directed to



RESO Certification Map

Definitions: Certified Legacy (on an older standard), Passed Current (technical testing is done), Certified Current (MLS has accepted terms of certification).

RESO Certifies Data Dictionary Compliance on the Web API for MLSs

There are approximately 540 MLS systems in the United States, 35 in Canada, and a small but quickly increasing number in Central and South America, Europe, and West Asia. The RESO Web API is the common data transport standard for MLS systems. Some systems still use the Real Estate Transaction Standard (RETS), but this is a deprecated legacy method of data transport that RESO discontinued certifying in 2018. | READ MORE ABOUT MLSs

The industry’s utilization of the RESO Web API is accelerating quickly. At least 90% of MLSs in the industry have RESO-certified Web API services. RESO tracks the migration to the improved Web API standard. If your organization is not listed on our leaderboard, please contact us to be included.


RESO Certifies a Lightweight Common Format for Non-MLSs

While the RESO Web API is primarily used by MLS data providers, other real estate organizations can benefit from having a standard, interoperable data format. RESO Common Format (RCF) hits the mark in a Data Dictionary JSON format. | VIEW THE RCF SPECIFICATION


The Certification Process

RESO’s certification process is highly automated. It is primarily processed between RESO and the technical vendor.

  1. Compliance Testing: RESO uses access credentials supplied by the applicant’s technology vendor and verifies standards conformance for the system.
  2. Certification: Applicants whose systems pass testing are asked to confirm results, accept certification terms and are then granted certification from RESO.

Cert Infographic Updated


Please have your technology provider contact RESO to initiate certification. They will complete technical testing with RESO staff, and we will notify your organization when your system is ready to certify. | TERMS AND CONDITIONS | PROCESSES AND POLICIES

In-Depth Certification Reports

RESO Analytics publishes in-depth reports on the metadata, standard resources and fields, custom local fields, data availability, and server performance of certified systems. Join the RESO Transport Workgroup and Certification Subgroup and its subgroups to learn more.

Certification Quick Facts

  • RESO currently certifies Web API Core 2.0.0, Data Dictionary 1.7 and RESO Common Format.
  • Uncertified U.S.-Based MLSs
  • MLSs that are owned and operated by a REALTOR® association are the most common certification recipients, because National Association of REALTORS® MLS policy requires compliance with RESO’s most recent standards, but certification can be obtained by independent MLSs, brokers and technology vendors.
  • The RESO Data Dictionary provides an industry-approved set of thousands of data fields and details that ensure all technology systems can work together. Data Dictionary certification tests technology systems to confirm that fields, enumerations and data format are in compliance with the standard.
  • Certification of RESO Web API servers ensures that technology systems can process requests from other systems and deliver responses in a standardized fashion. Standardized requests are run on an applicant’s server to ensure that they are processed correctly while returning data in the correct, standardized format.
  • The RESO GitHub is loaded with certification specifications.
  • The RESO Transport Workgroup and Certification Subgroup each meet monthly to discuss the technical details of certification.

Benefits of Certification

  • Fewer errors: The Data Dictionary provides simplified data integration, which means data can move between systems without losing information.
  • Lower maintenance costs: Data translation costs are reduced. You will spend less time fixing data issues.
  • Faster innovation, quicker iteration: By creating common standards, the need to create complex workarounds is eliminated. There’s more time to focus on cutting-edge technology improvements.
  • Efficient data sharing: An RCF endorsement gives brokers and their technology partners a better way to freely and efficiently share data between organizations, opening up opportunities for more certainty in technology planning.
  • Staying current, relevant: RESO’s mission is to help streamline the real estate industry’s technology. Getting certified allows you to focus on customer technology needs today and in the future.


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