Subject Line Tester
Test your email subject line for length, spam triggers, mobile compatibility, and engagement signals. Results update in real time.
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Subject line best practices
Your email subject line is the single most important factor in whether someone opens your email. It is also one of the first things spam filters analyze. A good subject line is clear, relevant, and avoids common spam patterns.
Keep it short
30-60 characters is ideal. Mobile devices show only ~40 characters. Put the most important words first.
Avoid spam patterns
No ALL CAPS, no multiple exclamation marks, no misleading claims like "guaranteed" or "free money".
Personalize
Including the recipient's name or company increases open rates by 26% on average.
Be specific
Numbers, questions, and concrete benefits outperform vague or generic subject lines.