Subject Line Tester
Paste a subject line. Get a 1–100 score, a breakdown of why, and three sharper alternatives.
How this works
The subject line is the only thing the recipient sees before deciding to open. It does about 80% of the work of the email — and it gets less than a quarter of the writer's time. This tool flips that ratio.
When you paste a subject, we run it through the same rubric used by the full HighConvertingEmails editor: curiosity gap, specificity, audience-fit, length, sender posture, and spam risk. You get a 1–100 score and a one-line explanation for each axis you fell short on.
Then we generate three alternatives that pick a different strategic angle — usually some mix of more specific, more concrete, and less generic. They're not always "better" for your audience; they're better starting points for your A/B test.
We don't pretend this predicts your actual open rate — nobody can do that without your sender reputation, list health, and history. What we can do is keep you out of the bottom half of subjects, which is where most under-performing emails live.
Want this on every email you send?
Sign up free and get unlimited runs of every tool, plus a one-screen editor that rewrites, scores, and generates subject lines, preheaders, and CTAs in seconds.