Paste a subject line. Get predicted open rate + AI-tells check + 3-5 better variants.
Paste your draft subject line. Get a predicted open-rate score, a list of specific problems, and 3-5 better variants ready to ship.
Mobile inbox preview cuts off subjects beyond 35-50 characters depending on client. 65% of opens are mobile (Litmus 2026 Q1). Subjects above 60 chars get truncated mid-thought and lose curiosity-tension. Strong subjects land at 4-7 words, 25-45 chars.
Specificity scores against an audience profile. "5 cold-outreach mistakes" is generic. "5 cold-outreach mistakes your competitors are making with PropStream lists" lands ONLY if the audience is real-estate investors using PropStream. The audience context lets the LLM grade for relevance, not just craft.
The score predicts quality relative to deliverability + persuasion benchmarks. Actual open rate depends on sender reputation (covered by the Email Deliverability Checker), list warmth, time of send, and inbox placement. Same subject sees 10% opens on cold lists and 40% on engaged ones.
Preheader is a 60-90 character second line that previews after the subject. Equally important. This tool grades the subject only — pair it with a preheader that completes the curiosity loop the subject opens.
Kompozy automates everything this tool estimates — multi-format generation, brand voice, scheduling across 9 platforms. Free 500-credit trial, no card required.