Spain's cadastre (the official property registry for land/buildings data) has a free
public API. The catch: it's SOAP/.asmx-era XML with three different services depending
on your input (reference, coordinates, or address), four different response shapes
discriminated by a counters block, business errors returned as HTTP 200 with the error
inside the XML, infra errors as HTTP 500 text/plain, decimal commas ("100,000000"),
and no documented rate limits or SLA.<p>I wrote up everything I hit while integrating it (applies even if you never use my
product): <a href="https://prediohq.com/guias/consumir-api-catastro-soap-json/" rel="nofollow">https://prediohq.com/guias/consumir-api-catastro-soap-json/</a><p>Predio is the wrapper I built on top: one JSON contract for the three inputs, typed
stable errors (404/422/402 always JSON), cache with serve-stale so the upstream's
availability isn't yours, and an MCP server (Streamable HTTP) so agents can call it
directly. Prepaid per-call pricing, 250 calls/month free, no subscription.<p>Honest caveats: Spain only (and not the Basque Country/Navarre, which run their own
foral cadastres); no ownership data (that's legally protected); if you need one lookup
a month, just use the official site — I wrote a comparison that includes "when not to
use us": <a href="https://prediohq.com/guias/api-catastro-comparativa/" rel="nofollow">https://prediohq.com/guias/api-catastro-comparativa/</a><p>Happy to answer anything about wrangling government SOAP into something agents can use.