Yes, that one's a bit tricky, isn't it? You might inspect the user-agent to at least try and only serve the font to browsers. You might also make sure that if t

Yes, that one's a bit tricky, isn't it? You might inspect the user-agent to at least try and only serve the font to browsers. You might also make sure that if there is a Referer, isn't not someone else's referer. I don't think it has to be foolproof to satisfy the terms of the license. It might also just be: you have to check the referer. If your website has technical issues such that sometimes the referer isn't available, you have to change it so it always is. Or host it on one of the approved third-party hosts referenced in the license.