Free subject line tester.
Improve your open rates.
Get an instant score, AI-powered rewrites, spam-trigger checks, and open rate estimates
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Learn moreFrom subject line
to campaign in minutes
No setup. No credit card. Paste your subject line, get your score, and send better emails — free.
Enter your email subject line
Type or paste any subject line — promotional, newsletter, transactional, re-engagement. Works for every email type.
Get your subject line score instantly
Our AI analyzes 40+ signals — length, language, emotion, urgency, spam risk — then gives you a score out of 100 with a plain-English breakdown.
Improve & launch
Get AI-powered rewrite suggestions, turn your subject line into a full email campaign, and send it directly with Constant Contact.
Built for email marketers
who care about results
Subject line scoring, deliverability checker, open rate predictor, AI rewrites, all in one tool.
Subject Line Score (0–100)
Instant 0–100 rating based on engagement signals, deliverability risk, word power, and emotional resonance — with a plain-English breakdown.
AI Subject Line Rewriter
5 AI-generated alternatives — shorter, more emotional, urgency-driven, or curiosity-based — each graded so you can pick the best one instantly.
Open Rate Predictor
See your predicted open rate range before you hit send. Calibrated against real benchmark data for your specific industry.
Industry Benchmarks
Compare your predicted open rate with other marketers in your industry. Know exactly where you stand.
Projects & History
Every subject line is saved. Organize by project, view trends over 30/90/all-time, and spot your winning patterns.
AI Email Builder
Love your subject line? Send it straight to Constant Contact's AI Email Builder — it'll craft a full campaign around it, ready for you to personalize and send.