Free tool · no login
Email Subject Line Tester
Score your subject line and get better alternatives.
A great subject line is the difference between opened and ignored. Paste your draft subject (and optional context) to get quick feedback plus five stronger alternatives. Free, no account required.
Free and rate-limited. Your text is sent to the AI to generate a result and is not stored. How we handle data.
Frequently asked questions
How does the subject line tester work?
It evaluates your subject for clarity, length, and curiosity, then suggests five higher-performing alternatives you can use right away.
Is it free and login-free?
Yes — it is free to use with no account, and rate-limited to keep it fair for everyone.
Where can I use these in my inbox?
Sign up for CometReplyAI to draft and send full replies (and compose new messages) directly inside Gmail, Outlook, and more.
More free tools
Use it where your email lives
CometReplyAI drafts replies in your own voice across Gmail, Outlook, Slack and more — you just review and send. Free to start, no credit card.