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The RESO Web API is the modern way to transport data in the real estate industry. It is built on well-known, open technology standards so that any organization can use it to deliver or receive data quickly and efficiently.

Companies are moving away from older, deprecated data transports like the Real Estate Transaction Standard (RETS) and transitioning to the RESO Web API for its superior technology benefits.

MLS Operators: View or download the Web API Transition Guide to speed up your team’s progress.

Technology companies report faster, more consistent and easier adoption of new technology systems after converting.

They also see much higher standardization of data via RESO’s certification standards for Data Dictionary on the Web API.

The Web API is real estate’s path to efficiency and streamlined technology experiences through modern standards. | MLSs CONVERTING TO WEB API

The RESO Web API moves the industry forward to widely adopted RESTful design in use by most industries today, promoting greater access to real estate information directly from the web, mobile, social and other HTTP-based applications.

RESO uses open standards and off-the-shelf tools that are supported across industries. By ensuring standards and protocols like OData at the core of the Web API’s functionality, industry incumbents and newcomers can be assured that they are building well-supported technology.

In the video, Michael Wurzer, CEO of FBS and RESO Board of Directors Vice Chair, explains the need for the industry to move forward with the transition to the RESO Web API.

See RESO Web API Commonly-Used Term and Definitions

RESO Members Offering Web API Services


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RESO Web API Utilization and Certification Statistics

RESO Web API Transition Report - June 2024RESO keeps track of which MLSs have converted completely to Web API, are in the midst of converting to Web API or are committed to converting.

We also manage a certification map, keep an alphabetical certification list and provide certification details through RESO Analytics.

Technical Specifications and Testing Rules

These documents describe RESO’s specifications. Because MLSs certify Data Dictionary standards on the RESO Web API, both sets of specifications are important for technical developers to understand. By downloading these resources, you confirm that you agree to the RESO EULA.

    Common Questions

    Why Web API Instead of RETS?
    RETS is an older standard that is proprietary to the real estate industry. It has been deprecated and is no longer supported by RESO because the industry needs to move to a more well-known technology standard.

    Can I get data from RESO through the Web API?
    RESO does not provide MLS real estate data. RESO creates data standards. Other organizations build technology based upon those standards. Data requests should be made to MLSs. MLSs owned and operated by REALTOR® associations are required by the National Association of REALTORS® to have production-level access available to their data via Web API.

    How do I get credentials to use the Web API?
    Access to data from the Web API is gained through local MLSs. After agreeing to an MLS’s data use and licensing policies, data recipients work directly with that MLS’s software provider or technical staff to receive credentials and instructions on how to access that MLS’s data.

    Do you have other questions?
    Please email us at

    Commonly-Used Terms

    API is short for Application Programming Interface. In a nontechnical sense, you can think of it as the panel on the back of a TV with ports and jacks to input and output media. It’s a set of standardized ways for technology systems to interact with each other. An API is an interface for access and delivery of data.

    Authorization identifies what kinds of data a user is allowed to access. To access data through an API, a data requestor supplies an authorization code – an API key or API token – and the user’s allowed level of data access is delivered through the API.

    Authentication identifies who is requesting data. An API needs to authenticate who is requesting data and identify which data they’re authorized to access.

    Endpoint is a web address where data can be accessed. An API service may have one or many endpoints where different kinds of data can be accessed.

    HTTP is Hypertext Transfer Protocol. It is the set of rules for transferring data between systems on the World Wide Web or within a network.

    JSON is a way to represent data that is simple for humans and machines to interpret. RESO’s Web API can return data to requestors in this format for ease of use.

    Metadata is “data about the data.” It is a user guide to explain what data is available and how it is organized. Metadata can be analyzed so that data requestors understand exactly what the data they access from an API will look like.

    OAuth is an open standard that allows for authentication and authorization in one step. It allows previously-identified users of systems (think Facebook and Google accounts) to log in to other APIs and get access to services quickly.

    OData is a protocol, or system of rules, for building an API and for transferring data through an API. RESO uses the OData V4 standard specification.

    Payload is a set of data which has a predetermined structure. An “IDX Payload” would include all of the fields needed for display on a real estate IDX website in a structured format that can be understood and easily consumed by the data recipient.

    Protocol is a defined system, process or set of rules.

    Query is a request a user makes to an API explaining what kind of data is needed. The RESO Web API can handle “live queries” that allow for immediate results in web applications.

    Replication is the copying of a database. Replicators initially pull an entire data set, and then continually request the most recent data changes to update their copy and keep it in sync with the primary database.

    REST is REpresentational State Transfer. It is a design for creating an API to efficiently communicate between systems. REST APIs, like the RESO Web API, use RESTful HTTP (web-based) requests to input, update, delete or get data through the API.


    The RESO Web API is the result of a collaborative effort from many industry experts who enlisted their time, vision and knowledge to the creation of this standard. We are enormously grateful for their contributions.

    Authors: Ashish Antal, Jeremy Crawford, Joshua Darnell, Sergio Del Rio, Bob Gottesman, Cody Gustafson, Cal Heldenbrand, Paul Hethmon, Peter Jang, Ivaan Nazaroff, Scott Petronis, Mike Pizzo, Demian Quinonez, Stuart Schuessler, Darrell Sher, Paul Stusiak, Mark Suchy.



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