PostcodeData.nl
Provide geolocation data based on postcode for Dutch addresses

Postcode lookup & Geolocation for the UK.
Postcodes.io API is a free Geocoding API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
Search, validate and geolocate UK postcodes. Retrieve the latest administrative and geospatial information for postcodes
Details from postcodes.io.

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Provide geolocation data based on postcode for Dutch addresses
The Postcodes.io API is provided by Postcodes.io (postcodes.io). Search, validate and geolocate UK postcodes. Retrieve the latest administrative and geospatial information for postcodes
Yes. The Postcodes.io API is listed in the Geocoding category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Postcodes.io API requires no authentication, so you can start making requests without signing up.
Yes. The Postcodes.io API supports CORS, so front-end JavaScript can call it directly.
Yes. The Postcodes.io API is served over HTTPS, so it's safe to use in production.