Linkchecker-markdown is a very fast Python module that checks internal and external website links using the raw Markdown before rendering by the static site generator. Avoid broken internal links by using a Git pre-commit hook to check all internal links upon each “git commit”.
In the top directory of the Markdown website repo, do:
git config core.hooksPath .git/hooks
add the file .git/hooks/pre-commit (no .py extension)
Related: global Git pre-commit for checking Python PEP8, etc.