Here’s an article from Moz Blog written by Cyrus-Shepard which I thought you might find of interest.

“There are literally hundreds of free SEO tools out there, so we want to focus on only the best and most useful to add to your toolbox. Tons of people in the SEO community helped vet the SEO software in this post. To be included, a tool had to meet three requirements. It must be: Widely used by the SEO community. Offers above-board value + actionable data. Actually, truly free.”

To read more head over to Moz Blog

Till next time,