First of all, like explained Replacing TinyMCE or CKEditor with Mosaico · voidlabs/mosaico Wiki · GitHub mosaico “save data” is currently composed by “2 objects” (metadata + content) than can be serialized to JSON. The output HTML is only an “export” and cannot be loaded back (just like when you save a webpage as PDF you can’t bring back the webpage html from the PDF).