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What is the RESO Web API?

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 RETS, and transitioning to the RESO Web API for its superior technology benefits. 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.

See a list of MLSs converting to 100% Web API.

Michaal Wurzer, RESO Vice Chair and CEO of FBS, explains the need for the industry to move forward with the transition to the RESO Web API:

The RESO Web API moves the industry forward to widely-adopted RESTful design in use by most industries today. The Web API promotes 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’re building technology that will be well-supported in the future. 

See RESO Web API Commonly-Used Term and Definitions

RESO Web API 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 About the Web API:

    Why Web API Instead of RETS?

    RETS is an older standard that is proprietary to the real estate industry. It has been deprecated (it’s no longer being supported or improved at RESO) because the industry needs to move to a more well-known technology standard. While RETS still works for many applications, all technology evolves. RETS created great value for 20 years, and the conversion to Web API is underway.

    Can I get data from RESO through the Web API?

    RESO does not provide MLS real estate data. RESO creates the standard for the data, and other organizations build technology based upon it. 

    Brokers and technology companies should go directly to MLSs to request data via the Web API. 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 will come from local MLSs. After agreeing to an MLS’s data use and licensing policies, data recipients will 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?

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    Commonly-Used RESO Web API 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.

    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.

    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.

    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.