RESO Web API — REST/JSON on OData v4, OAuth, calls MLS directly (no local DB duplication); NAR requires REALTOR-association MLSs to provide production-level Web API access

Claim. The RESO Web API is the modern industry standard: REST/JSON on OData v4, OAuth-based, calls the MLS directly with no local duplication. NAR requires REALTOR-association-owned MLSs to provide production-level Web API access. Data is gained through local MLSs after agreeing to their data-use and licensing policies.

Quote.

"Access to data from the Web API is gained through local MLSs. After agreeing to an MLS's data use and licensing policies, data recipients work directly with that MLS's software provider…"

Source. reso.org/reso-web-api, accessed 2026-06-21.

Confidence. Verified.

Caveats. "Production-level Web API access" is the NAR mandate; individual MLSs vary in how complete or current their implementation is, and licensing tiers (IDX/VOW/back-office) control which fields are actually exposed even on a compliant API.

Implication / use. The modern feed mechanic. Any "we built on RETS" claim is legacy; any "we built on RESO Web API" claim still depends on the per-MLS DLA scope.