I’ve added some info about creating draft blog posts to Micro.blog’s Micropub API help page. It also documents a new
preview URL that can be used by third-party apps to send the user to a preview web page, with an option to finish publishing the post.
The preview renders the Markdown text, but does not process it through Hugo, so it might not exactly match the published HTML on your microblog in some cases. I plan to further improve this in the future to send it through Hugo.
Along with the new preview URL for the API, I’ve also fixed a bug creating draft posts with the JSON flavor of Micropub.