NS, only trains.
Transport for The Netherlands API is a free Transportation API that requires apiKey authentication, is only available over HTTP and has unconfirmed CORS support.
Discover APIs, learn how to use them, try them out interactively, and sign up to acquire keys.
Details from ns.nl.

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The Transport for The Netherlands API is provided by NS API Developer Portal (ns.nl). Discover APIs, learn how to use them, try them out interactively, and sign up to acquire keys.
Yes. The Transport for The Netherlands API is listed in the Transportation 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.
Yes. The Transport for The Netherlands API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Transport for The Netherlands API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
No. The Transport for The Netherlands API is only available over plain HTTP, which browsers block on HTTPS sites. Call it from a server instead.