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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteFor a new MLS data integration, choose the RESO Web API. RESO describes RETS as deprecated and unsupported, and ended RETS certification in 2018. A particular MLS may still have a RETS feed during a transition, so confirm that provider’s migration timeline and feed details before planning a build.
What is the difference between RESO Web API and RETS?
They are ways to exchange MLS data, but they are at different points in their lifecycle. RESO’s Web API is its current transport standard; RETS is a legacy transport that RESO says is deprecated and unsupported. RESO identifies Web API Core 2.0.0 as currently certified and says it discontinued RETS certification in 2018. RESO certification
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| Area | RESO Web API | RETS |
|---|---|---|
| Status | RESO’s current transport standard; Web API Core 2.0.0 is listed as currently certified by RESO. Source | Deprecated and unsupported by RESO; RETS certification ended in 2018. Source |
| Technology | Uses RESTful principles, JSON and OAuth; RESO also highlights OData and other widely supported web technologies. Source | An older, real-estate-specific transport that RESO says is unsupported. Source |
| Data structure | Commonly used with the RESO Data Dictionary, which standardizes resources, fields and lookup values while allowing local fields. Source | Historical specifications remain available in RESO’s specifications list. Source |
| Best fit | New integrations and migrations targeting RESO’s current standard. | A temporary or existing dependency where a particular MLS feed has not yet moved; confirm the local sunset plan with the provider. |
RESO says Web API is intended to support interoperability among MLS, broker, agent and consumer technology systems. That describes the standard’s aim, not a quantified guarantee about implementation cost, speed or reliability. RESO Web API overview
What the Data Dictionary does—and does not do
The Web API is the transport: it defines a standardized way for software to request and exchange data. The Data Dictionary supplies a shared vocabulary and structure for that data, including resources such as Property, Member, Office and Media, the fields in those resources, and the lookup values associated with fields. The two standards are related, but one does not replace the other. RESO Data Dictionary
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RESO identifies Data Dictionary 2.0 as current. Its inventory includes more than 1,700 fields and 3,100 lookups, but RESO says most organizations are not expected to adopt the complete dictionary and full adoption is not required for certification. Local market fields can be represented. For an integration, establish which resources and fields the MLS actually exposes, which follow standard definitions, and how its local fields are delivered. RESO Data Dictionary RESO certification
How widely has Web API been adopted?
RESO’s live certification page, accessed October 4, 2026, reports that at least 90% of MLSs in the industry have RESO-certified Web API services. The page’s displayed update context says “Data updated 10/02/2026”; these are RESO-reported figures, not an independently audited count. RESO certification
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RESO’s live Web API Transition Leaderboard, also accessed October 4, 2026, reports subscriber coverage in two separate categories: 62.4% of U.S. subscribers are covered by feeds converted to Web API, while feeds committed to conversion cover 76.4%. These percentages measure subscriber coverage, not the share of MLS organizations, and “converted” and “committed” are distinct categories. RESO Web API Transition Leaderboard
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A migration affects more than the endpoint: applications and downstream vendors may depend on current feed behavior, data fields, media links and update assumptions. RESO’s Web API Transition Guide, published May 24, 2023, frames conversion as preparation, communication, scheduling and execution with the MLS’s technology vendor and affected customers. The specific implementation and timetable depend on the MLS and feed provider. RESO Web API Transition Guide
- Inventory dependencies. List applications, internal workflows and downstream vendors using RETS or another feed mechanism. Identify what each consumes and who owns it.
- Confirm the target service. Ask the MLS or its technology provider which Web API and Data Dictionary versions are available, which resources and standard fields are exposed, and how local fields are represented. RESO lists Web API Core 2.0.0 and Data Dictionary 2.0 among its current certification offerings. RESO certification RESO Data Dictionary
- Set up access. Obtain the required credentials, authorization, production entitlements and terms from the provider. Ask whether a parallel-running period is available rather than assuming one.
- Test actual feed behavior. Validate parsing, filters and pagination, updates, media links and error handling against the provider’s documented endpoint. Check workload-specific assumptions with the provider; the standard alone does not establish local rate limits or operational behavior.
- Agree on transition controls. Coordinate stakeholder communications, schedule, cutover, monitoring and rollback arrangements with the MLS and vendor. Confirm any sunset date directly rather than inferring it from RESO’s general RETS status. RESO Web API Transition Guide
Where do developers get MLS data?
RESO creates standards; it does not supply MLS listing data. For production access, contact the relevant MLS and meet its credential, permission and terms requirements. RESO notes that REALTOR®-association-owned MLSs are required by NAR policy to provide production-level access through Web API; this does not mean access is automatic for an individual developer. RESO Web API overview
For development, RESO’s FAQ identifies a Web API Developer Reference Server created in collaboration with Austin Board of REALTORS®, RESO and Zillow’s Bridge Interactive API service. It describes access to the previous year’s listing data from Austin’s Unlock MLS. Check the server’s current availability and terms before relying on it. RESO FAQ
RESO certification checks whether a system processes standardized requests and returns data in the expected standardized format. RESO lists open-source testing, client SDK and reference implementation tools alongside its certification offerings. Certification can help establish standards conformance; it does not tell you which fields, permissions or service terms a specific MLS will provide. RESO certification
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