Keyword Research Tools - ASO

Hey guys. I've got a task at my hand that requires a keyword research tool for ASO (both google playstore and iOS) so I was wondering if you have any services that I might use?

Please note I'm going to research niches that don't have an app yet - so I cannot connect the app like some tools require.

So far the only good one I found is keywordtool.io but their subscription is pretty much expensive.
Let me know reviews about this one or any other tool you know. Thanks and have a nice day!

Apptweak is great, has unique features and does not cost too much
You could also try ASOdesk, which has interesting traffic volume predictions

App Promotion said:

Apptweak is great, has unique features and does not cost too much
You could also try ASOdesk, which has interesting traffic volume predictions

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Apptweak is at $25 for only 50 keywords as it says in the plan. It also says 2 Your Apps so I'm not sure if I will be able to do a keyword research without entering the app, but however 50 keywords will be too little for my research.