guillermofc

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.

I wrote up everything I hit while integrating it (applies even if you never use my product): https://prediohq.com/guias/consumir-api-catastro-soap-json/

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.

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": https://prediohq.com/guias/api-catastro-comparativa/

Happy to answer anything about wrangling government SOAP into something agents can use.