Cartes.io vs Postcodes.io

Cartes.io is an open-source platform for creating and sharing custom maps with markers, letting anyone plot points, GeoJSON shapes, and metadata without running their own server. Reading public maps and markers needs no signup — write access is optional and controlled per map, either open to anyone or gated behind a token issued when the map or marker is created. The API returns JSON by default and GeoJSON on request, and the project ships official Python and NPM packages alongside its hosted instance at cartes.io.

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.