I don’t know of one that’s you can leave running and track it throughout your day but maybe KeyKey would be a good way to test and track it at intervals https://keykey.ninja/. Source: about 2 years ago

If you're fine with recording, then you want to look towards transcribing apps (I don't have names, but when I looked for one in Play Store a while back, there's a bunch) and use that. You can then use something like wordcounter.io or even google docs to count the words. Source: over 1 year ago

Look at your competitors pages and create a better page - What I mean by this is look at how many words they're using on their page (use wordcounter.io for this, paste it all in), how many images or videos they have on the page, how many times they mention the main keyword and how many outbound links they have. If they're #1, they must be doing something right, so make a note of all this and either match it or go... Source: about 3 years ago