Subject Line A/B Tester
Enter two subject lines and we'll predict which one will achieve a higher open rate based on patterns from 5M+ cold emails.
Want AI-optimized subject lines?
Sales.co generates and A/B tests subject lines automatically, using AI trained on millions of cold emails.
Optimize with Sales.co →How the A/B Tester Works
This tool scores subject lines on factors proven to impact cold email open rates: length (3–6 words optimal), personalization (merge tags boost opens by 26%), spam triggers (promotional words reduce inbox placement), question format (questions get 14% higher opens), and capitalization (sentence case outperforms title case).
The predicted open rate is based on aggregate patterns from cold email campaigns. Your actual results will vary based on list quality, sender reputation, and sending time. Use this tool to compare relative performance — the subject line with the higher score is more likely to outperform.