Hi all, sorry for the slow reply.
We only add sites to the whitelist if they (the sites themselves) have official documented public APIs. We don't actively monitor them, though, so some sites can get whitelisted and then remain on the list even when they're not hosting APIs.
However, someone recently started abusing PythonAnywhere by setting up tens of thousands of junk accounts with code to "watch" a YouTube video. That meant that we had to review our blanked whitelisting of YouTube.com, and we discovered that it no longer seems to have an API hosted there -- its API is now at www.googleapis.com
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If there is a documented API that is on a different hostname, however, do let us know -- we just need a link to its docs.