Norwegian Government Open Data.
Open Government, Norway API is a free Government API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
Felles datakatalog – data.norge.no er det offentlige nettstedet som gir oversikt over beskrivelser av datasett, begrep, api-er og informasjonsmodeller. Innholdet blir levert av ulike virksomheter, offentlige og private. Det er Digitaliseringsdirektoratet som er ansvarlig for drift og utvikling av n…
Details from data.norge.no.

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Yes. The Open Government, Norway API is listed in the Government 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 Open Government, Norway API requires no authentication, so you can start making requests without signing up.
Yes. The Open Government, Norway API supports CORS, so front-end JavaScript can call it directly.
Yes. The Open Government, Norway API is served over HTTPS, so it's safe to use in production.