A simple lookup from file name/extension to MIME/media type and vice versa, generated from mime-db, which in turn is compiled from IANA, Apache and nginx's MIME types.
This is a source-only package, containing a single class, MimeTypes, which will be compiled into your library/application under the root namespace.

The easiest way to get it, is to install the source package from NuGet.org.

Otherwise you could just pull the source file from GitHub.

Get the MIME/media type for a file name/extension by using the MimeTypes.TryGetMimeType or MimeTypes.GetMimeType methods:

if (MimeTypes.TryGetMimeType("awesome-file.json", out var mimeType))
{
    // mimeType == "application/json"
}

MimeTypes.GetMimeType("awesome-file.json"); // "application/json"

When calling GetMimeType, if a mapping for the given file extension doesn't exist, it will fall back to MimeTypes.FallbackMimeType, which is set to application/octet-stream by default.

To get all available file extensions for a MIME/media type, you can call MimeTypes.GetMimeTypeExtensions. This returns back an IEnumerable<string> of all the available files types for the specified MIME/media type.