The Yaost SEO plugin is one of the most popular Wordpress plugins. It allows you to add SEO title, meta description, and meta keywords to each post and page of your site. In case you update your website, Yaost also adds Open Graph meta data, Twitter Cards, Sitemaps and ping search engines.
Yes, you can purchase separate subscriptions for each site. However if you bought a Video SEO license before January 7th 2013, you have an unlimited license. Also, if you bought any Agency license before August 12th 2013, you have an unlimited license.WordPress SEO Plugins Yoast SEO