A Multiple Listing Service (MLS) is a private database created, maintained, paid for, and used by real estate professionals to share property listing information and facilitate cooperation among brokers to help their clients buy and sell homes. MLS databases generally contain valuable listing information such as addresses, prices, photographs, property descriptions, amenities and features, listing statuses, and other transaction-related information. This data can be distributed to participating brokers via a variety of data access frameworks, including but not limited to Internet Data Exchange (IDX), Virtual Office Websites (VOW), and Brokerage Back Office (BBO) feeds.
What is Internet Data Exchange (IDX)
The Internet Data Exchange, or IDX, is primarily a consumer-facing method of displaying MLS listing information. IDX allows MLS Participants to authorize the electronic display and delivery of their listings by other Participants through approved media such as websites and mobile applications.
The central purpose of IDX is property marketing and consumer search. A consumer visiting a real estate brokerage website can typically search for active and sold (when permitted) properties using criteria such as location, price, property type, bedrooms, bathrooms, and other characteristics. IDX is therefore closely associated with public-facing real estate websites such as brokerage and agent websites and search portals.
The data displayed through IDX is subject to MLS rules concerning what information can be displayed, how it must be attributed, and how the listings can be presented. Such policies were first established back in 2000 under NAR Policy Statement 7.58 and then adopted by MLSs nationwide.
What is Virtual Office Website (VOW)
A Virtual Office Website, or VOW, is another consumer-facing use of MLS information, but it is fundamentally different from IDX. A VOW is a website or feature of a website through which a Participant provides brokerage services to consumers with whom the Participant has first established a broker-consumer relationship as defined by applicable state law. Think of a Virtual Office Website as essentially an online brick-and-mortar for the brokerage.
A VOW can therefore support a more comprehensive online brokerage experience. The consumer may receive access to more detailed listing information and functionality within a website, such as off-market listing data, sold price history, and listing details that may not be permitted in public IDX displays. Such access is granted after the consumer has completed the formal registration process, established a lawful broker-consumer relationship, in addition to any other requirements required by the MLSs’ and NAR’s VOW policies and applicable local rules.
What is Broker Back Office (BBO)
Broker Back Office, or BBO, is designed primarily for internal brokerage operations rather than public property marketing.
Under NAR Policy Statement 8.7, BBO Data includes all real property listing and roster information from the MLS database, subject to exclusions for MLS-only fields and content that the MLS does not have sufficient licensing rights to distribute through BBO.
Permitted BBO uses include brokerage management systems, CRM and transaction-management systems, agent productivity tools, brokerage ranking and reporting tools, and certain marketplace statistical analyses in conformance with NAR MLS Policy Statement 7.80, which allows for certain public distribution.
For example, a brokerage could use BBO data to create an internal dashboard showing listings, market activity, productivity information, or other information useful to the brokerage and its affiliated Subscribers. BBO information can also be used in certain CRM and transaction-management environments involving bona fide clients, subject to the policy requirements.
Unlike IDX, BBO is not primarily intended to create a public-facing property search website. Its focus is on helping a brokerage operate its business and provide services to its affiliated professionals and clients. Approved BBO data is only to be used and accessed by a participant and the subscriber(s) affiliated with said participant, and never by a consumer.
Differences Between the Feed Types
Use case
The most fundamental difference between IDX, VOW, and BBO is the intended use.
| Feed Type | Primary Purpose | Who Uses It? | Typical Examples |
|---|---|---|---|
| IDX | Public-facing property marketing and search | Consumers and the general public | Brokerage websites, property search portals, and mobile apps |
| VOW | Providing MLS information to consumers who have established a broker-consumer relationship | Registered consumers working with a brokerage | Online property research, detailed home searches, client-facing brokerage platforms behind a registration wall |
| BBO | Internal brokerage operations and business functions | Brokers, agents, and authorized brokerage personnel | CRM systems, transaction management, productivity tools, reporting, brokerage analytics |
Data Fields
The data fields available through each data framework can differ. IDX typically focuses on information appropriate for public display. VOW can provide a broader and more detailed MLS search experience because access is connected to an established brokerage relationship and controlled by the Participant. BBO can contain an even broader and more detailed set of listing and roster information for authorized internal purposes. However, even BBO does not automatically include every field in the MLS. MLS-only fields and content for which the MLS lacks sufficient licensing rights are specifically excluded from the BBO definition.
Importantly, there is no universal list of fields that every MLS must provide identically through every feed. Local MLS rules, data licensing agreements, property types, state law, and third-party content licenses can affect the actual data available.
Approval Process
The approval process differs based on the purpose of the feed.
For IDX, the Participant and any technology provider must meet the MLS’s requirements for IDX display and data use. Some examples of display requirements include accurate listing brokerage attribution, brokerage branding, and data display update frequencies.
For VOW, the Participant must establish the required broker-consumer relationship framework and operate the VOW under the applicable policy. The VOW also has requirements concerning consumer registration, terms of use, privacy, and MLS compliance. For example, MLSs may require consumers to update or reconfirm their passwords every 90 days.
For BBO, the Participant is entitled to use BBO Data for defined BBO purposes. However, the MLS can impose reasonable licensing provisions and fees, and a Participant’s designee may be required to sign a license agreement, which clearly outlines its use case.
Access to MLS data
Access to MLS data is generally tied to an MLS Participant’s authorized rights and the particular use for which the data is being requested. A Participant may use MLS data directly or designate a technology vendor, like AnyProp, to facilitate an authorized use.
NAR’s One Data Source policy states that MLSs must offer a Participant a single data feed consistent with the Participant’s licensed authorized uses. At the Participant’s request, that feed can be provided to the Participant’s designee, like AnyProp, who may use it only to facilitate the Participant’s authorized uses.
This distinction is important because a technology vendor, like AnyProp, does not simply receive unrestricted ownership or control of MLS data. Our ability to access and use the information generally derives from the Participant’s authorized relationship and the applicable MLS license or agreement. MLSs may also require vendors, like AnyProp, to enter into data license agreements establishing security requirements, permitted uses, and other conditions.
In conclusion, IDX, VOW, and BBO should be viewed as different data access frameworks of MLS information. IDX focuses on public-facing property marketing, VOW connects consumers with an established brokerage relationship with more detailed MLS information, and BBO supports internal brokerage operations and related authorized business functions. Although the exact implementation varies among MLS organizations, all three are governed by the fundamental principle that MLS information must be accessed and used according to the Participant’s authorized rights, applicable MLS policies, licensing restrictions, and the intended purpose of the data.
How AnyProp can help
AnyProp is an approved data vendor nationwide for the three primary MLS data use cases; IDX, VOW, and BBO. We have years of experience helping our clients strategize and apply for the correct data access framework according to their use case.
Additionally, for most brokerages and proptech companies, managing MLS data across multiple markets can quickly become a significant technical and operational challenge. Each MLS can have different data structures, field definitions, display requirements, approval processes, attribution rules, and compliance requirements. As a company expands into additional markets, maintaining these individual integrations can consume substantial engineering and operational resources.
AnyProp helps simplify this process by providing a unified, normalized real estate data platform through a single RESO-standardized API. The benefit for an engineering team is that AnyProp handles much of the complexity behind the data layer. Instead of building and maintaining separate integrations for each MLS, your developers can work with a consistent and normalized data structure across markets. AnyProp also provides data-quality services such as address normalization, media deduplication, polygon geospatial filtering, and field-level validation.
Compliance is another important part of the value proposition. MLS compliance does not end once the licensing agreement has been signed and approved. Depending on the use case and market, there may be requirements around which listings can be displayed, how listings are attributed, what disclaimers must appear, and which fields can be exposed. AnyProp coordinates MLS approvals and helps manage these market-specific requirements, reducing the amount of MLS-by-MLS compliance work that a brokerage and proptech company’s internal team would otherwise need to manage. Our MLS profiles endpoint supplies disclaimers and basic compliance elements to your team during their implementation of the approved MLS feeds.
Ultimately, AnyProp allows brokerages and proptech companies to focus on building their products rather than building and maintaining an MLS data infrastructure from the ground up. By combining MLS data access, compliance coordination, normalization, data quality, and multiple delivery options into one platform, AnyProp can help companies enter new markets more efficiently while reducing the engineering and operational overhead associated with managing multiple MLS relationships and integrations.
