RETS, the Real Estate Transaction Standard, is the XML-based protocol that carried multiple listing service data between systems for roughly two decades before the RESO Web API replaced it. Version 1.8 is the last widely-deployed revision. RESO formally retired it in favour of an OData-based successor, and it remains in production at major data distributors years afterward.
RETS
RETS was how American property listing data moved for about twenty years. An XML-based request and response protocol with its own login, search and metadata semantics, it predates the conventions most developers now take for granted and requires a client written specifically for it. The Real Estate Standards Organization declared it end-of-life and directed the market to the OData-based RESO Web API as its successor.
- Bespoke, not RESTful - RETS defined its own transaction model rather than composing HTTP conventions, so tooling never generalised and every integration was purpose-built.
- Formally superseded - The RESO Web API and Data Dictionary replaced it, and NAR’s certification mandate applies to the successor, not to RETS.
- Still in production - The State of US Real Estate APIs found Trestle documenting RETS 1.8
alongside its certified OData surface, with a dedicated
scope=retsOAuth scope issued next to the modern one. Retirement was announced; decommissioning was not completed.
The entry earns its place as a documented case of a standard that was properly replaced and did not go away. The successor is better designed, formally certified and industry-mandated, and the predecessor still answers requests because hundreds of independent cooperatives and their vendors each had to migrate on their own schedule and cost basis. Anyone modelling a standards migration should assume a long tail measured in years, and should budget for running both surfaces rather than for a cutover.
For an integrator the practical read is simpler: if a provider still advertises RETS, that is a signal about the age and layering of its stack, not merely a legacy footnote.
Referenced in API Evangelist papers
This standard shows up in my published research. These reports read the machine-readable evidence provider by provider — and put this standard in the context of a real sector.
The State of US Real Estate APIs
Formally superseded by the RESO Web API and still carrying production traffic — Trestle documents RETS 1.8 alongside its certified OData surface, with a dedicated scope=rets OAuth scope.
