The Multimarkdown {{TOC}} Table of Contents generation is supported if you are using MultiMarkdown as your Markdown generator.
There is a slight gotcha, however, due to the fact that the double curly braces conflict with Drafts’ template engines use of those markers for URL encoding. To get the table of contents inserted in your preview, you must escape it to prevent URL encoding handling it before MultiMarkdown gets a hold of it - so use \{{TOC}} (note leading backslash excape character.
So, this Markdown in Drafts:
\{{TOC}}
# Header 1
# Header 2
Will generate this preview:
