Email Subject Line Tester
Test your email subject lines for deliverability, engagement, and spam risk. Get an instant score with actionable feedback.
Email Subject Line Best Practices
Keep it under 50 characters
Most email clients truncate subject lines on mobile at 30-40 characters. Front-load the most important information so it is visible even when cut off.
Avoid spam triggers
Words like "free," "guaranteed," "act now," and excessive punctuation can trigger spam filters. Write naturally and avoid sales language in the subject.
Create curiosity or urgency
The best subject lines make the reader feel they will miss something if they do not open. Questions, numbers, and specific benefits all drive curiosity.
A/B test every send
Send two variants to a small portion of your list, then send the winner to the rest. Even small open rate differences compound over time.
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