Google Trends

Trends reports interest on a scale of 0 to 100 against the peak for whichever terms and period you selected. It shows no absolute volume at all, so two terms are comparable with each other and with nothing else.

Switch the source from web search to YouTube search and it tells you how demand for a topic moves on the platform you publish to, which is the version worth checking before committing a video to an idea. It is also the quickest read on seasonality, on whether a topic is fading, and on whether a spike is real or one news story.