RESO Web API vs RETS
The BrokerFold Team — Product + Engineering
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RETS and the RESO Web API are two generations of the same plumbing: the standards that move listing data from an MLS to the software that displays it. RETS — the Real Estate Transaction Standard — is the legacy protocol, built around XML and periodic batch downloads. The Web API is its successor, a modern query interface that RESO adopted in RETS’s place when it retired the old standard in 2018. For an agent, the difference is not academic: it predicts how fresh your website’s data is and how quickly your platform can grow with you.
What RETS was built to do
RETS solved the problem of its era: getting a copy of the MLS out of the building at all. A vendor authenticated, requested records in bulk, and maintained a local mirror by pulling updates on a timer — workable, but heavy. Every vendor parsed slightly different field names for every board, updates arrived in scheduled batches rather than on demand, and keeping a mirror faithful required constant reconciliation. A generation of listing websites inherited that shape: data that was hours old on a good day, and field mappings that had to be rebuilt board by board. None of this made RETS a bad standard for its time — it made cooperative data portable at all, which is why it survived nearly two decades — but its assumptions belong to an era when a nightly refresh felt generous and nobody expected a sold status to reach a phone in minutes.
What the Web API changed
The RESO Web API turned replication from scheduled bulk pulls into precise, continuous queries: a vendor asks for exactly the records that changed since its last checkpoint and gets them back in a standard web format. Paired with the RESO Data Dictionary, which standardizes field names across markets, it removed most of the per-board translation work that made RETS integrations slow to build and slower to extend. The practical ceiling moved: sync cadence in minutes instead of hours, and new-board expansion measured in adapter work rather than reverse-engineering.
Is RETS deprecated? Yes — with a long tail
RESO ended support for RETS in 2018, and no new development happens on it. What kept the question alive is the tail: MLSs ran legacy endpoints alongside new ones for years so vendors could migrate without breaking, and some vendors simply never moved. In Canada the migration is effectively settled where it matters — TRREB distributes over a Web API platform, as unpacked in TRREB data feeds, and the other major feeds an agent’s website depends on speak the modern standard too. A stack still anchored to RETS in 2026 is not “proven technology”; it is deferred maintenance.
The buying signal hiding in this comparison
Ask any website vendor one plain question: which protocol do your board integrations use today? The answer sorts the market fast. A vendor consuming Web API feeds first-hand controls its own sync cadence and field coverage; a vendor still bridging through RETS-era tooling — or reselling someone else’s integration built on it — inherits the batch-era limits no matter how modern the website on top looks. Freshness questions, missing-field questions, and “can you add my board?” questions all trace back to this layer, which is why it earns a line on any serious provider comparison sheet.
The short version
RETS moved copies of the MLS on a timer; the Web API streams precise changes on demand. The standard flipped in 2018, the industry followed, and the vendors who moved early are the ones whose sites answer a status change in minutes. When you evaluate platforms, you are also choosing which side of that migration your website lives on.
Frequently asked questions
Is RETS officially dead?
As a standard, yes — RESO retired it in 2018 and all new certification work moved to the Web API. As infrastructure, it died slowly: individual MLSs kept legacy endpoints running for years while vendors migrated, which is why the question still comes up. The direction has been one-way for a long time.
Does the protocol my vendor uses really affect my website?
Yes, in ways visitors can see. Batch-era integrations tend to refresh on a schedule measured in hours, so status changes lag; query-based Web API replication supports a cadence measured in minutes. Field coverage and how quickly a vendor can add a new board follow the same divide.
How is the RESO Data Dictionary different from the Web API?
The Web API moves the data; the Data Dictionary names it. One is transport, the other is a shared vocabulary so that a field like list price means the same thing across markets. A board can adopt both together, which is the modern pattern, and serious vendors rely on the pairing.
Keep reading
- RESO Web API The RESO Web API is the modern standard for moving MLS data between boards and the platforms that display it. What it replaced and why it matters.
- RESO Data Dictionary The RESO Data Dictionary is real estate's shared vocabulary — standard field names and values that make MLS data mean the same thing across markets.
- How to choose an IDX provider The Canadian gotchas to check before signing an IDX contract: board approval timelines, Schedule B paperwork, lock-in, and who keeps your leads.
- TRREB data feeds TRREB distributes listing data through three lanes — IDX, VOW and DLA — over the AMPRE RESO Web API. A vendor's first-hand map of what each carries.