
.NET package versions, metadata and search.
NuGet API is a free Development API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
The NuGet Server API is a set of HTTP endpoints that can be used to download packages, fetch metadata, publish new packages, etc.
Details from learn.microsoft.com.

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The NuGet API is provided by Microsoft Learn (learn.microsoft.com). The NuGet Server API is a set of HTTP endpoints that can be used to download packages, fetch metadata, publish new packages, etc.
Yes. The NuGet API is listed in the Development 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 NuGet API requires no authentication, so you can start making requests without signing up.
Yes. The NuGet API supports CORS, so front-end JavaScript can call it directly.
Yes. The NuGet API is served over HTTPS, so it's safe to use in production.