Email Subject Line
Tester
Score your subject lines before you hit send. Get instant feedback on open rate potential, spam risk, and engagement.
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Our AI Email Marketing Kit includes proven subject line formulas, welcome sequences, cold outreach templates, and newsletter frameworks.
How to Write Email Subject Lines That Get Opened
The average person receives 121 emails per day. Your subject line has about 3 seconds to convince someone to open yours instead of deleting it. Here's what the data says works.
The Science Behind Great Subject Lines
Research from over 12 billion emails shows that the best-performing subject lines share common traits: they're between 30-50 characters, use specific numbers, create curiosity without being clickbaity, and feel personal. Our email subject line tester scores against all of these factors.
5 Proven Subject Line Formulas
- The Number Formula: "[Number] ways to [achieve desired outcome]" — e.g., "7 ways to double your email open rates this week"
- The Curiosity Gap: "The [unexpected thing] about [familiar topic]" — e.g., "The surprising truth about cold email outreach"
- The How-To: "How to [achieve goal] without [common pain point]" — e.g., "How to grow your list without paid ads"
- The Social Proof: "How [person/company] [achieved result]" — e.g., "How Sarah generated $12K from one email sequence"
- The Question: Ask something your reader is already wondering — e.g., "Are you making these 3 email marketing mistakes?"
What to Avoid in Subject Lines
Spam filters have gotten sophisticated, but certain patterns still trigger them. Avoid ALL CAPS, excessive punctuation (!!!), spam trigger words like "free money" or "act now", and misleading RE: or FW: prefixes. Our tester checks for all of these.
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