Lint your markdown files with flymake (built into Emacs) and the best markdown linter, markdownlint, AKA mdl (the ruby version that's easy to install and configure).

But note that mdl is a little slow, so you might want to only run flymake on save.

(add-hook 'markdown-mode-hook #'flymake-mode)
(require 'flymake-mdl)
(add-hook 'markdown-mode-hook 'flymake-mdl-setup)