Email Subject Line Tester
Score subject lines on length, spam triggers, and engagement signals. Mobile inboxes truncate at ~30–40 chars; spam filters punish certain phrases.
Subject line
Preview header
Score
—
out of 100
Email subject line rules that actually work
- 30–50 chars for mobile inbox visibility (most opens)
- Avoid spam triggers like FREE, WIN, $$$, ALL CAPS
- One exclamation max — more triggers filters
- Numbers + specifics outperform vague benefits
- Personalization tokens ({first_name}) lift open rate 15–25%