Email Subject Line Tester
Test your email subject lines for spam triggers, length, and mobile readability.
How to Use This Tester
Enter your subject line: Type the email subject line you want to test.
Review the score: Get an instant score based on length, spam triggers, personalization, and other factors.
Check spam triggers: See if your subject line contains words that might trigger spam filters.
Preview on mobile: See how your subject line appears when truncated on iPhone (most emails are opened on mobile).
Follow recommendations: Get specific tips to improve open rates.
Why Subject Lines Matter
Your subject line determines whether your email gets opened or ignored. 47% of email recipients open emails based solely on the subject line. Another 69% report emails as spam based on the subject line alone.
Length matters more than ever because 81% of emails are opened on mobile devices. iPhone Mail shows approximately 35-40 characters in portrait mode. If your key message isn't in those first 40 characters, it might as well not exist.
Spam trigger words ("FREE!!!", "ACT NOW", "LIMITED TIME", all caps, excessive punctuation) can land your carefully crafted email in the spam folder where it will never be seen. Even if it makes it to the inbox, aggressive language reduces trust and open rates.
Personalization (using the recipient's name or other custom data) can increase open rates by 26%. Urgency words ("today", "ending soon", "last chance") create FOMO but must be used genuinely—fake urgency destroys trust and increases unsubscribes.
Subject Line Best Practices
- Front-load value: Put the most important words first (they might be all that appears on mobile).
- Use one emoji max: One emoji can increase open rates. Multiple emojis look spammy.
- Avoid all caps: "AMAZING OFFER" screams spam. "Amazing offer inside" is professional.
- Test personalization: A/B test "[Name], check this out" vs generic subject lines.
- Be specific: "Your order has shipped" beats "Update on your order". Specificity builds trust.
- Create curiosity gaps: "We made a mistake (and you benefit)" makes people want to learn more.