There are both free and paid tools, and you can spend a fortune every month licensing the paid ones.
You can also spend a huge amount of time looking at these solutions, delving into reports, slicing and dicing the data they provide, and being overwhelmed by the sheer volume of data available, rather than working on the tasks that will actually improve your SEO and drive more organic traffic and conversions.
Which tools produce the best ROI for your time and money? Some of my favorite SEO tools; http://searchengineland.com/tools-tools-everywhere-seo-tools-worth-time-222123
Via Antonino Militello