Compare explicit provider regions at one common period

Requires API-key or first-party session authentication and a current account in the default-off server cohort. Valid current membership does not require a new paid subscription. Existing API quotas still apply. Responses are private, no-store. Unknown and repeated query parameters are rejected. This contract does not indicate source activation, deployment or an SDK release. Use-specific, unexpired reviewed Zillow rights are checked before parcel resolution or repository/cache access. Denied/unknown rights return explicit unavailable metric values, not substitute data. Each metric exposes actual regional geography/variant and freshness; regional values do not become parcel estimates or residual inputs. Up to five distinct region IDs use one dataset/accepted snapshot and common month. First ID is the reference. Value gaps retain a missing reason; incompatible regions are not converted to comparable parcel data. Alternatively provide parcel_id, metric and period (optional window_months) instead of dataset_key and region_ids. Property geography is resolved only by the server. County/metro/national comparisons require compatible metric definitions, units and variants, one requested month and an explicit captured acceptance cutoff. Each dataset retains its own snapshot provenance. Missing mappings, permissions and variants remain unavailable; mixed query forms are rejected.