adresse.data.gouv.fr vs Postcodes.io

The Base Adresse Nationale's API Adresse geocodes and reverse-geocodes French addresses for free with no API key, backed by Etalab and IGN's data.geopf.fr infrastructure (the older api-adresse.data.gouv.fr host still answers directly and does not redirect). Requests and responses use the GeoJSON FeatureCollection format, with each result scored for match confidence and enriched with INSEE city codes, postcodes, and population. A live Origin-header probe confirms open CORS (Access-Control-Allow-Origin: *), so it works directly from browser JavaScript with no proxy.

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.