Google Keywords Planner is a part of Google Adwords program. This is the most popular tool to find the exact search queries with search volume about what people use.
GKP has recently enhanced and came up with several new features. This "free" tool is also capable to extract search queries your potential customers can use to reach your website. It gives you the bidding difficulty in search marketing for these keywords and other suggestions according to your preference to make your campaign more profitable.
Keyword Planner, however, is restricted to Google searches only and can not give Bing and other search engine data like Semrush.