SEMRUSH is great tool to find keyword , its free also.But you may use google adword to find keyword related to your website
Google Keyword Planner Tool, SEMrush, and keywordtool.io are some great tools to find the best keyword.
I do not know whether i can link back to my article here where i explained how to find long tail keyword tools and found some great results.
specific tool for specific niche helps and i checked most of the free tools which we daily use.
If you want to find my article let me know.