Type your subject line and preview text — the score, signals, and inbox previews update live.
Switch between Gmail, Mobile, and Outlook tabs to see how your subject truncates on each.
Review the signals panel — fix spam triggers, add power words, refine until your score is 70+.
FAQ
Scores of 70–100 indicate a well-optimised subject line — correct length, no spam triggers, strong power words, and engagement signals like numbers or questions. Scores of 50–69 are passable but can be improved. Under 50 means the subject has significant issues that will reduce open rates.
The ideal length is 41–50 characters — long enough to convey value, short enough to display in full on most desktop clients. On mobile, only ~30 characters are visible, so place your most important words first. Subjects under 20 characters often feel abrupt, while subjects over 60 characters are truncated on most clients.
Classic spam trigger words include: free, urgent, guarantee, winner, cash prize, click here, act now, buy now, limited time, and special offer. Using $ symbols, excessive exclamation marks, or ALL CAPS also increases spam scores. Modern filters use context, so one trigger word rarely causes filtering — but several together significantly raise your spam probability.