Probably doesn’t follow the spec very closely.

It doesn’t require you to put a double space in the end off a line to get to the next. This is similar to a lot of other implementations you see on web pages.
But it does at least follow through with single level ordered and unordered lists (bullets and numbering) and even automatically adds a bullet when you press Shift+Enter
Also, single line code and code blocks, work.
Then there is the usual italics and bold and even a quote block.

It also converts most of them while you type, instead of you having to wait until sending it, which is better than UIs that don’t even have a preview button. I like Preview buttons.

I’d say, it’s good enough for casual stuff.