Best SEO tool that I can use

Hey! I am the founder of a relatively new start-up with only a few clients, and for some reason unable to get more clients. Tried using viral reels, audios, etc. as well as have also tried using SEMRUSH, MozBar and SEO Quake, but at one point it requires you to pay for their plans (which is fair ), but as I don't have that many clients on board currently, I want to know from you all if there is any free SEO tool that I can use for now? Any suggestions appreciated! TIA.