You should ask a proper question. You said tools but tools means what? Do you want to know everything about SEO. Such as keywords research, and other plugin or anything?
Its not full question to give you best suggestion because you need to define that your website is in wordpress or custom because if your website is in wordpress then can find many plugins (Free and Paid) which can help you in SEO like YOAST ..... But if your website is custom then you should use any external tools which can give you about all information to optimize your website to beat your competition like SEMrush.
I have bee using Yoast for years and very happy with it! A good alternative is All in One SEO Pack. The free version is good enough...