Markdeep is a great project and supports a lot of impressive features. However, if you care about conforming to CommonMark, I would request you to try out TeXMe. I initially wrote TeXMe for me and my friends. After a Show HN post about it, it has found a lot of other users too. TeXMe has a very minimal feature set but it cares about CommonMark.

TeXMe on GitHub: https://github.com/susam/texme

TeXMe Demo: https://opendocs.github.io/texme/examples/demo.html

Detailed comparison between TeXMe and Markdeep: https://news.ycombinator.com/item?id=18314175