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 old api-adresse.data.gouv.fr host now 301-redirects there). 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.