Subject Line Scorer
Score a cold email subject line as you type. See what is costing you opens — length, spam triggers, vagueness — and what to change.
Scores as you type · runs in your browser
Type a subject line above to see your score instantly.
What makes a good cold email subject line
A good cold email subject line earns an open from someone who didn't ask to hear from you — in under half a second, sitting alongside 50 to 200 other subject lines in a crowded inbox. The job isn't to sell; it's to create enough curiosity or relevance that clicking feels lower-cost than ignoring it.
Length matters more than most people realise. A line that truncates at "We help companies like yours impro..." gets dismissed. One that fits cleanly in the preview pane — 28 to 50 characters — gets read. Mobile is now where most cold email is first seen, which makes length a technical constraint as much as a stylistic one. The word count equivalent is 3 to 7 words.
Spam trigger words kill deliverability before a human ever sees the line. Words like free, urgent, and guarantee route messages to junk automatically, or lower your sender score over time. A subject line that passes the spam filter and reads like it was written for one specific person — not a thousand — is the standard worth aiming for. Specificity, whether through a number, a question, or a merge tag, is the single most reliable lever for improving cold email open rates.