API Découpage Administratif (API Geo) vs Postcodes.io

Etalab's Découpage Administratif API looks up and cross-references France's administrative hierarchy — communes, EPCIs, départements, and régions — by name, postcode, SIREN, or geographic coordinates, with no API key required. The stored api.gouv.fr/api/geoapi.html link had gone stale, 301-redirecting to a generic data.gouv.fr listing page instead of the live docs; the real service and interactive documentation are hosted at geo.api.gouv.fr. A live Origin-header probe against the real /communes endpoint confirms open CORS, reflecting back whatever Origin is sent.

Postcodes.io is a free, open-source (MIT-licensed) UK postcode lookup and geocoding API: it validates postcodes, reverse-geocodes coordinates to the nearest postcode, and returns administrative geography — ward, constituency, parish, LSOA/MSOA, and more — sourced from the ONS Postcode Directory. It's built and maintained by Ideal Postcodes as a free public service, with a paid Ideal Postcodes product available for teams needing rooftop-level precision or fresher data.