Use Markdownlint
Markdown has become my preferred way to write documentation. I use it for the documentation for open source projects, like READMEs, Change Logs etc. In additional to that I use if for longer technical specifications, since it is so simple to work with and Markdown is so easy to use it lets me focus on the content I want to write.
Writing to many different documents and with the focus on content I sometimes make mistakes in my Markdown, but since Markdown is well formatted, it is actually possible to parse it and say something about the formatting - and here Markdown linters can help you.
I am unclear on the story behind the Markdown linters I have found, but it seems as if the first implementation was in Ruby, the project is markdownlint/markdownlint and offers the executable mdl.
A newer alternative is the Markdown linter implemented in Node, this project is DavidAnson/markdownlint. The Node implementation does not hold it’s own executable, there you have to use the executable markdownlint implemented in igorshubovych/markdownlint-cli.
Both implementations implement a set of rules Ruby implementation and Node implementation respectively.
This documentation is nice to have close at hand when you get started.
I wrote up a blog post where I compare the rulesets of the two.