Dear,
SEO tools can be used on three stages. First of all, if you are using SEO tools for link building then we will not recommend you to go for black hat techniques. 2015 would be tough to SEO's as only genuine SEO effort will bring success. Secondly, tools can be used for tracking your performance like Ahrefs, ProRankTracker and so on. Finally, for SEO research Google trends, Market Samurai and other tools would also be used.