A gem version of @bhardin's SEO Jekyll tool
gem install jekyll-seo
Use the -k flag to input specifc keywords to check against, and the -p flag to specify the path to the post.
$ jekyll-seo -k "welcome to jekyll" -p _site/jekyll/update/2015/04/05/welcome-to-jekyll.html
Analyzing Post: _site/jekyll/update/2015/04/05/welcome-to-jekyll.html...
Article Heading: true (1)
Page title: true (1)
Content: true (1)
Meta description: false (0)