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)