Closing as not a bug, this is all the save/load machinery. I tried to design it so Closure Compiler would omit it if it wasn't used, but it proved rather difficult to do that. I don't think it's too important anyway, since most servers transmit HTML, JS and CSS in compressed format, so the actual transmitted size will be roughly equivalent to the size of zipping the file. An empty project exports to ~93kb minified, and compresses down to just 30kb, so I think in practice the runtime script will be about as big as one or two images from your project.