Most copy dies at the first line. Paste a headline, subject line or hook and Whetstone grades it the way a direct-response copywriter would: curiosity, specificity, promise and awareness fit.
Does the first line create enough tension, curiosity or self-interest that the next line gets read?
Concrete nouns, numbers and details beat abstractions. Vague headlines get skimmed past.
A headline that asserts ("amazing results") is weaker than one that demonstrates the result.
The right headline for an unaware reader is the wrong headline for someone ready to buy.
Got more than a headline? Grade the full piece.