I get the feeling that many web #API designers avoid #multipart file uploads because in most frameworks and also client libraries, it sucks. But it does not have to. It's actually the best we have to transfer multiple files in one request and also quite efficient when using a sane parser or modern browsers. It just has a bad reputation from complicated and slow parsers written for emails that have to carry decades of technical depth. Modern HTML5 multipart/form-data is not the same thing.