KaTeX already provides pre-rendering of math. If you want to start with Markdown you can use Pandoc. Then you can get TeX, HTML, and even Word formats from the

KaTeX already provides pre-rendering of math. If you want to start with Markdown you can use Pandoc. Then you can get TeX, HTML, and even Word formats from the same source. This project seems to only work with one particular editor, as well.