I tried using this headline analyser https://www.isitwp.com/headline-analyzer/ but honestly, none of the stories that achieved high grades on the headline analyser did well, so I just use my own judgement now. The best thing, is to probably make sure you're using the strongest headline vs subhead. I wrote about it here: https://medium.com/the-shortform/one-little-tweak-and-my-story-did-better-than-expected-5a81126cf7dc