How to write a subject line

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Ran a little experiment recently. I tested some popular cold outreach subject lines with an online subject line rater.

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“Quick question, Will” scored a 96/100—almost perfect. But if it landed in *my* inbox, I’d delete it in a second.

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Scoring well ≠ converting well.

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What actually works? Based on what we’ve seen with Rocketbrew:

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• ✍️ 3-4 words is the sweet spot – Shorter subject lines (under 5 words) tend to have higher open rates.
• ✍️ Personalization beats clickbait– “Quick question” is vague. Instead, make it about them: reference their work, interests, or recent LinkedIn activity.
  
  • “Your post on AI”
  • “Shoptalk 2025 next month”
• ✍️ No ‘email-y’ words – Avoid words like "free," "discount," or "meeting request." Instead, make it sound like a note from a colleague.
• ✍️ Questions work—when specific – Instead of “Quick question”, try:
  
  • "Scaling your AE team?"
  • "Is [Company] exploring X?"

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A subject line’s job isn’t just to get opened—it’s to make answering feel easy.