1. Keyword Planner

Google keyword tool widely used in the over all world for keyword research.  

2. Ubbersuggest

Ubbersuggest tool shows you the search volume, SEO difficulty, paid difficulty, and CPC. 

3. SEMrush Keyword Magic Tool

The SEMrush Keyword Magic Tool gives information from a global database of more than 20 billion keywords 

4. Keyword Sheeter

Build up a comprehensive list of keyword ideas 

5. AnswerThePublic

There are 3 billion Google searches every day, and 20% of those have never been seen 

5 Amazing Free Keyword Research Tools For SEO