All in One SEO Analyzer by AIOSEO

A free Chrome extension from the AIOSEO team that analyzes the page you are on and helps tune it for search engines. It looks at meta descriptions, titles, keywords and content structure, then returns an SEO score that reflects how well the page is optimized, with a higher score meaning a better-optimized page. It works on any website, so it suits quick checks on your own pages as well as pages you are comparing against. Its publisher has a good record with no history of violations.