Multiple Listing Services (MLS) are vital to the real estate industry. They serve as databases where brokers and agents can share property listings, collaborate on deals, and access important market information. But behind this smooth exchange of data lies a major challenge: interoperability.
Interoperability refers to the ability of different systems, platforms, or software to work together seamlessly. In the world of MLS, this means ensuring that listing data, user information, images, and documents can be shared across different tools and services without conflicts or loss of quality. It also means that data should be structured in a way that both humans and machines can understand it clearly.
Over the years, various standards and practices have emerged to support this goal. In this article, we’ll explore what interoperability means in the MLS environment, why it matters, and what standards currently guide the industry toward seamless data sharing and integration.
Why Interoperability Matters in MLS
Interoperability is important for many reasons, especially in an industry where agents, brokers, tech companies, and consumers all rely on fast, accurate, and consistent data.
When an MLS lacks interoperability, the result can be poor user experiences, duplicated work, broken software features, and even legal compliance risks. Real estate professionals may have to enter the same listing into different platforms manually. Consumers may see outdated or incorrect property details. Developers may spend hours trying to connect different systems that were never designed to work together.
Interoperability ensures that:
- MLS data can be accessed and understood by third-party apps, CRMs, and marketing tools.
- Agents can easily syndicate listings to national portals or partner brokerages.
- Software developers can build better user experiences with fewer technical barriers.
- Consumers receive timely and reliable property data on every platform they use.
For MLS organizations, supporting interoperability also helps future-proof their systems and keeps them competitive in a fast-moving digital world.
The Role of RESO in Promoting Standards
The Real Estate Standards Organization (RESO) plays the most important role in advancing interoperability standards for MLSs. RESO is a nonprofit organization that creates and maintains open standards to streamline data sharing across the real estate industry.
Many of the current interoperability improvements in MLS systems are thanks to RESO’s efforts. The organization works with MLSs, brokers, tech vendors, and others to design consistent frameworks for how data should be structured and transmitted.
Two of RESO’s most important contributions are:
- The RESO Data Dictionary
- The RESO Web API
RESO Data Dictionary
The RESO Data Dictionary is essentially a universal language for MLS data. It defines standard names, formats, and meanings for all the fields that might appear in a property listing or transaction record.
For example, a field like “bedrooms” might be labeled differently across various MLS platforms – one might call it “Bedrooms,” another “Beds,” and a third “BR.” This creates confusion when trying to integrate or compare data from multiple sources.
The Data Dictionary sets a standard label, such as BedroomsTotal, along with rules about its data type, allowable values, and description. The same applies to thousands of fields covering everything from square footage and listing status to heating type and price history.
By following the Data Dictionary, MLSs and developers can reduce the amount of custom coding needed to interpret each system’s data. It also ensures consistency when syndicating data to partner platforms.
RESO Web API
The RESO Web API is a technology standard that allows systems to exchange data over the Internet in a secure and modern way. It replaces older technologies like RETS (Real Estate Transaction Standard), which were harder to implement and less flexible.
The Web API is built on RESTful principles, which are widely used in the software industry. This means developers can use familiar tools and languages to access MLS data, speeding up integration and reducing errors.
With the RESO Web API, third-party applications can query MLS listings, receive updates, or push new information in real-time. For example, a CRM system might use the API to pull a broker’s active listings and display them within their dashboard, or a mobile app might update listing prices live as they change in the MLS.
The API supports authentication, authorization, and encryption, helping ensure data security and compliance with privacy rules.
MLS Grid and Regional Cooperation
In addition to RESO, other initiatives are pushing interoperability forward by promoting regional cooperation. One major example is the MLS Grid – a collaborative project by several MLSs aimed at simplifying how data is shared and standardized.
The MLS Grid offers a single point of access to standardized data from multiple MLSs. This allows national vendors and brokerages to integrate with many MLSs at once, rather than building custom connections to each one.
It’s a practical example of how shared standards can improve data access and reduce technical complexity. Projects like MLS Grid also encourage more MLSs to adopt RESO-compliant systems, further boosting interoperability across the industry.
Common Interoperability Challenges
Even with standards in place, real-world implementation can be messy. Many MLSs still face challenges that make interoperability difficult. These include:
Legacy Systems
Some MLSs still use outdated software that doesn’t support modern APIs or the RESO Data Dictionary. This makes it harder to adopt new tools or meet standard requirements.
Partial Adoption of Standards
Not all MLSs implement RESO standards in full. Some may only use part of the Data Dictionary or may modify standard field names for internal use, defeating the purpose of having a universal language.
Custom Fields and Local Rules
MLSs often add custom fields or business rules to reflect local market needs. While these are helpful locally, they can cause conflicts or confusion when trying to share data nationally.
Data Quality Issues
Interoperability depends on clean, accurate data. If an MLS has missing values, inconsistent formats, or outdated records, it becomes harder to share that data meaningfully with others.
Security and Compliance
Some integrations fail to meet strict privacy or cybersecurity requirements, creating legal risks or exposing the MLS to potential data breaches.
Industry Efforts to Improve Interoperability
Improving interoperability is not just a technical challenge – it’s an industry-wide effort. Multiple stakeholders play a role in driving the adoption and refinement of standards:
MLS Organizations are expected to implement RESO-compliant APIs, standardize their databases, and audit their data quality regularly.
Brokerages and Franchises advocate for better data access and often pressure MLSs to adopt common standards so they can offer better services to agents and clients.
Tech Vendors and PropTech Startups build tools on top of MLS data and rely on reliable, standardized APIs to deliver innovative products.
Associations and Policymakers support legislation and best practices that encourage openness, data sharing, and consumer transparency.
The Future of Interoperability in MLS
As technology continues to evolve, the need for robust interoperability will only grow. Several future trends are likely to shape how MLS systems operate and share data:
AI and Machine Learning Integration
Modern tools that offer pricing models, property recommendations, or market forecasts all rely on large volumes of clean, standardized data. Strong interoperability makes this possible.
Mobile and On-Demand Services
Consumers and agents expect real-time access to MLS data from mobile devices. APIs and standards will play a key role in supporting responsive, connected applications.
National MLS Models
Although most MLSs remain regional, there is a push toward more unified, cross-regional systems. Interoperability is the first step toward creating systems that function across borders.
Blockchain and Smart Contracts
As real estate explores blockchain technologies, interoperable systems will be needed to connect property records, title systems, and transaction histories securely.
Conclusion
Interoperability standards are the foundation of a connected, efficient, and forward-looking real estate industry. For MLSs, this means adopting RESO standards like the Data Dictionary and Web API, reducing reliance on outdated systems, and working collaboratively with industry partners.
While challenges remain, the growing adoption of open standards is a positive sign. By continuing to prioritize consistency, security, and accessibility, MLSs can better serve their members, reduce operational headaches, and help real estate evolve into a smarter, more integrated digital ecosystem.
Whether you’re a broker, tech developer, or MLS executive, investing in interoperability is no longer optional – it’s essential for the future of the industry.
