Some of the tools commonly used for researching keywords include:

1. Google Keyword Planner: Provides keyword ideas and traffic estimates.
2. SEMrush: Offers keyword research, competitive analysis, and more.
3. Ahrefs: Helps identify keywords, analyze backlinks, and track keyword rankings.
4. Moz Keyword Explorer: Provides keyword suggestions and metrics like difficulty and opportunity.
5. Ubersuggest: Offers keyword ideas, content ideas, and competitor analysis.
6. KeywordTool.io: Generates keyword ideas from Google autocomplete.
7. SpyFu: Helps spy on competitors' keywords and ad campaigns.
8. Google Trends: Shows the popularity of keywords over time.
9. AnswerThePublic: Provides keyword suggestions based on common questions.
10. KWFinder: Helps find long-tail keywords with low SEO difficulty.