Subject Lines

Description

Writes and optimizes subject lines for cold emails. Use when the user asks to "write a subject line", "improve my subject line", "subject line ideas", "A/B test subject lines", "open rate optimization", "my open rates are low", or needs help with email subject lines specifically. Also triggers on "subject line best practices", "what subject line should I use". Do NOT use for writing full email ...

What this skill does

1. 1Generates 3-5 subject line options per email using four proven formulas: personalized, curiosity gap, direct value, and the 2-word AI-generated format.
2. 2Applies cold email subject line rules: 2-4 words, all lowercase, no spam trigger words, no exclamation marks, always relevant to the email body.
3. 3Recommends an A/B test pairing two contrasting styles (e.g., personalized vs. curiosity) with clear rules for minimum sample size and which metrics to judge.
4. 4Distinguishes subject line treatment by sequence position: Email 2 reuses the original subject in the same thread, Email 3 gets a fresh subject.
5. 5Provides formula-based AI prompts that generate 2-word subject lines calibrated to each prospect's business context.

When to use

• Your open rates are below 30% and you need to test whether a different subject line style makes a difference.
• You've written the email body and need 3-5 subject line options to match the value prop and persona.
• You want to set up a proper A/B subject line test with correct sample sizes and success criteria.
• You're writing Email 3 in a sequence and need a new subject line that doesn't repeat the original.

Frequently asked questions