Is there a Google tool to check or to compare two keywords? I would like to know if "string1" is more searched than "string2".
Or how many times "string1" is search in last 30 days, or something like this.
Google Trends is the tool you are looking for. To compare the interest over time in bananas vs apples for example, view https://trends.google.com/trends/explore?q=banana,apple.