Nominatim vs PostalCodes

Nominatim provides worldwide forward and reverse geocoding built entirely on OpenStreetMap data, needing no API key — only a descriptive User-Agent or Referer header identifying the calling application (the policy states a stock HTTP-library User-Agent will not do). The public instance at nominatim.openstreetmap.org mainly exists to power the search bar on openstreetmap.org and runs on donated servers with very limited capacity: its usage policy caps requests at an absolute maximum of 1 per second, forbids autocomplete-style querying outright, and requires results to be cached on the caller's side. Bulk geocoding is restricted rather than banned — a smaller one-time task is permissible on a single thread and a single machine, with distributed scripts disallowed and anything running longer than a day capped at 4 requests per minute. The policy points larger users first at commercial third-party providers, and the largest at running their own Nominatim instance.

Postalcodes.info is a free postal-code reference for 123 countries and more than 1.8 million records. No key is needed. The JSON endpoint /api/v1/postal-code/{country}/{code} returns the place name, region and coordinates for one code. Per-country exports come as CSV, JSON or XLSX. The JSON API sends Access-Control-Allow-Origin: *, so a browser can call it directly. The /search autocomplete endpoint does not send that header.