In episode 183 of Semantic Mastery's weekly Hump Day Hangouts, one participant asked what is considered over-optimization as far as SEO is concerned.
The exact question was:
What is considered over optimization as far as SEO? Having the exact title match the keywords I am trying to rank? Or tags? Besides Yoast, is there a site where I can input my post or article and check it to see if I am over optimized?