You can already view most used words for different mood ratings on your mood trends page.

In terms of trying to ascertain your mood rating and pull tags out of your mood note, we want the process of rating your day and choosing which tags to add to be a conscious one, a thoughtful process for the user to undertake. I’d rather not leave a very important question, “how did you feel today?” up to an algorithm that could get it wildly wrong.

Of course, the reason we have an API is for users to explore other approaches, so you could certainly write something that does this for yourself. But it’s not an approach we’re interested in building in.