Keyword planning is most important while writing a SEO optimized article. You can use following tools : -
1. SEMRush: - If you are serious about SEO then SEMRush is a must. It comes with all the essential tools for keyword research. Apart from that you also get competitor, backlinks, trends, etc. as well. It is a bit expensive then other keyword planning tools out now but as per features provided by SEMRush its a great deal to go for.
2. Google Adwords Keyword Planner: - If still you don't want to spend money in then go for keyword planner. As it is a google product it comes with all the access to keywords, trends, etc. live stats to Google's database.
After I got a permanent earning every month. I subscribed to SEMRush monthly plan. Just after subscription I am getting excellent results. As per my experience I will suggest you to go for SEMRush otherwise Google Keyword Planner is best choice.
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I am currently pursuing High School and planning to pursue career in Computer. Currently, I work on one of my blog - JTech Articles.