
Portugal Government Open Data.
Open Government, Portugal 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.
Portuguese open public data portal: download, share and reuse open data from the State and local authorities
Details from dados.gov.pt.

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The Open Government, Portugal API is provided by dados.gov.pt (dados.gov.pt). Portuguese open public data portal: download, share and reuse open data from the State and local authorities
Yes. The Open Government, Portugal 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, Portugal API requires no authentication, so you can start making requests without signing up.
Yes. The Open Government, Portugal API supports CORS, so front-end JavaScript can call it directly.
Yes. The Open Government, Portugal API is served over HTTPS, so it's safe to use in production.