EXPERIMENTAL (beta): this tool may change or be withdrawn without notice; do not build critical workflows on it. Measure the asking-vs-transaction price spread for a Polish city or county: how far the median asking price per m² of apartments for sale sits above (or below) the median apartment transaction price per m² from the RCN registry. spread_pct = (asking − transaction) / transaction × 100. The spread can be NEGATIVE (asking below transaction) in premium-secondary cities — that is a valid answer, not an error. Address by location (city name → resolves to a county) OR teryt (4-digit county code; 6-digit = dzielnica where available, today Warszawa's 18 districts, otherwise truncated to the county; teryt wins when both are given). Both sides need at least 5 samples or the result is suppressed. For marketType='all' (the default), sale offers are a mix of primary and secondary market, so the transaction denominator covers the whole market. With marketType='secondary' or 'primary', both the asking and transaction sides are narrowed to that single market segment. Not comparable across cities with different as_of dates (RCN publication lag varies by county). Asking and transaction prices come from different sources, so the spread is an approximation. Coverage is county-level only (miasta na prawach powiatu) plus Warszawa's 18 districts, and further limited to cities with asking-sale data. A town inside a larger powiat (e.g. Sandomierz, Pruszków), a non-Warszawa city district, or an osiedle does NOT resolve and returns a 404 that lists matching units as candidates (a candidate is not a coverage guarantee) — do not pass such names. Unless the location is a major city you already know is covered, call list_price_spread_locations FIRST to get valid names, or pass a 4-digit county TERYT. Optional areaBucket restricts both sides to an apartment area range in m2 (e.g. '40-50'). Area ranges are NOT additive — a bucket does not sum back to 'all'. The transaction-price denominator uses the market median. Note: median/average prices are market-based — fractional ownership shares and non-market deeds (public tenders, foreclosures, privileged/subsidized sales) are excluded from price aggregates. Transaction counts and coverage stay complete.