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Email Subject Line Tester
Review subject line length and wording, flag common spam terms, and preview mobile/desktop truncation.
Subject Lines
Scoring Factors
Length28–50 chars is optimal for most clients
Spam riskAvoid trigger words that bypass filters
CuriosityQuestions and gaps drive opens
PersonalizationUse "you" / "your" to feel direct
UrgencyTime-sensitive language boosts opens
NumbersSpecific numbers increase credibility
EmojiStand out visually in inbox (use sparingly)
Type subject lines on the left to instantly score open rate potential and see inbox previews.
Email Subject Line Tester
The Email Subject Tester scores your subject lines across 7 key open-rate factors: length, spam word risk, curiosity gap, personalization, urgency, numbers, and emoji. It also simulates how your subject appears in a mobile inbox (~40 chars), desktop client (~60 chars), and Gmail (~77 chars) — so you can see exactly what subscribers read before deciding to open.
What's the ideal subject line length?
Industry data consistently shows 28–50 characters drives the highest engagement. Mobile email clients truncate at ~40 characters, so the most critical words should appear first. Avoid writing long subjects hoping the preview text will save it.
Do spam words really affect deliverability?
Yes, but modern spam filters are more sophisticated than a simple word list. High-risk words like "FREE!!!" or "BUY NOW" combined with other signals (sender reputation, link count) dramatically increase spam folder placement. Avoiding them is always safer.
Get more from Email Subject Line Tester
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Need help with inputs or downloads? Read the help page.