There are a ton of SEO sites free tool and even more that aren’t free. Usually the free ones are just teasers for the paid tools. I’ve collected links to free tools that I have found relevance by using them. Beyond the tools to optimize a sites SEO its important to have at least a foundational understanding of what is SEO. It isn’t what it used to be, sites would simply pick the keywords they wanted to rank for and then repeat that keyword over and over sometimes at the bottom of a page or behind an image where online a search engine would find them. Keywords allowed gamification of rankings and Google stepped away from keywords focusing more on backlinks, links that pointed back to your site.
Before you jump onto these resources do spend sometime reviewing the links below. There are common mistakes and sites can be penalized for appearing to game the system. The first step to proper SEO is quality content. Fix errors and give them something of value too link too.
In order to do SEO here are some backlinks to a few sites that I’ve found useful.