What tool do you want?
Be able to provide HTML and generate Markdown or provide Markdown and generate HTML.

Describe the solution you'd like
Pretty much like https://codebeautify.org/html-to-markdown

Is their example of this tool in the wild?
Tons, but ones like https://codebeautify.org/html-to-markdown & https://www.convertsimple.com/convert-html-to-markdown/

Additional context
The ability the save the content as either a .html or .md file would be nice.