Email Subject Line Tester

Subject lines are the single highest-ROI piece of copy in any email. A professional gets 120+ messages a day, spends 2-3 seconds per subject line, and decides open-skip-delete against a wall of competing subjects. Yours is not evaluated in isolation — it's evaluated against everything else that landed in the same window. The Email Subject Line Tester scores against that reality, not against an abstract style guide.

Every line is graded on six factors out of 30: specificity (does it tell the reader what they'll actually get), curiosity gap (is there a hook only the open can resolve), length and scannability (does the meaningful content survive mobile truncation at 30-40 characters), emotional trigger (curiosity and FOMO beat manufactured importance), inbox differentiation (does it look different from the other 119 subjects), and spam safety (the words, punctuation, and patterns that route you to promotions). The scoring is explicit so you can see exactly which factor your draft is failing.

Ten alternatives come back ranked, not just listed. Rank one isn't a guess — it's the highest scoring across the six factors with a primary strength noted. The A/B test recommendation pairs two variants that use different psychological triggers (curiosity vs urgency, specificity vs social proof) so whichever wins tells you something about your audience that applies to every future email, not just this one.

There's also a preview text pairing for the top three. Most senders treat preview text as automatic — first line of the body, whatever shows up — when it's actually the second-most-important piece of inbox real estate. The skill writes preview text that complements the subject line rather than repeating it, because a subject and preview that say the same thing waste both. None of this includes emoji crutches or fake "Re:" prefixes. You'll get told if your draft uses them.