Why I built it
I write in Markdown all day: specs, notes, posts, the front matter that drives half my tooling. I could not find an editor that showed me all three of the things I care about at once. Every one of them made me pick.
The pretty editors hide the syntax, so I could not tell whether a stray character was breaking a list. The plain text editors show the syntax and nothing else, so I was reading raw markup to check how a document would land. And nearly all of them treated YAML front matter as either invisible or as body text to be mangled, which is a problem when the front matter is the part your automation reads.
So I built the thing I wanted. WordMD shows formatted output and raw source side by side, keeps them in sync as you scroll, and treats front matter as a first-class part of the document you can open and edit without leaving the app.
It is free. I use it every day, which is the best endorsement I can offer.