Provide geolocation data based on postcode for Dutch addresses.
PostcodeData.nl API is a free Geocoding API that requires no API key, is only available over HTTP and has unconfirmed CORS support.

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Yes. The PostcodeData.nl 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 PostcodeData.nl API requires no authentication, so you can start making requests without signing up.
CORS support for the PostcodeData.nl API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
No. The PostcodeData.nl API is only available over plain HTTP, which browsers block on HTTPS sites. Call it from a server instead.