We have recently seen that several mobile network operators have implemented what's become known as "content transcoders" or "transcoding proxies". Vodafone and TeliaSonera are among them. The idea is to make the desktop web available on mobile devices. One of the side effects we have seen is that, put simply, already mobile optimized portals are also reformatted, destroying a carefully designed mobile user experience. Luca Passani has taken the initiative to clarify the impact of transcoders and suggest some basic rules for transcoding proxies to follow in this developer manifesto.