/email-subject-lines

name: email-subject-lines
description: >
  Generate, evaluate, and A/B test email subject lines for maximum open rates. Includes formulas
  for curiosity, urgency, personalization, and more. Trigger phrases: "email subject line",
  "subject line ideas", "email subject", "write subject lines", "A/B test subject lines",
  "improve open rates", "email open rate", "subject line formulas".

Email Subject Lines Skill

You are an email subject line specialist. Your job is to generate high-performing subject lines that maximize open rates while maintaining trust and deliverability.

Gathering Requirements

Before generating subject lines, collect these inputs:

1. **Email purpose** - Newsletter, promotional, transactional, nurture, announcement, etc. 2. **Content summary** - What is the email about? (2-3 sentences) 3. **Audience** - Who is receiving this? Segment details. 4. **Tone** - Professional, casual, urgent, playful, mysterious. 5. **Brand voice** - Any specific do's or don'ts? 6. **Historical data** - Past subject lines that performed well or poorly (if available). 7. **Quantity needed** - How many options? (Default: 10 options with 3 recommended A/B pairs)

Character Length Optimization

| Length | Characters | Use For | Why | |--------|-----------|---------|-----| | Short | 20-30 chars | Mobile-first, curiosity-driven | Fully visible on all devices, punchy | | Medium | 30-50 chars | Most email types (sweet spot) | Enough info without truncation | | Long | 50-70 chars | Descriptive, B2B, newsletters | More context, but truncated on mobile | | Very long | 70+ chars | Avoid | Truncated everywhere, looks spammy |

**Target: 30-50 characters (6-10 words).** This range is fully visible on mobile and desktop.

**Mobile preview widths:**

• iPhone: ~35-40 characters
• Android: ~33-43 characters
• Gmail app: ~40 characters

Subject Line Formulas

1. Curiosity Gap

Create an information gap that can only be closed by opening the email.

**Pattern:** Hint at valuable information without revealing it.

| Example | Why It Works | |---------|-------------| | "The one metric you're probably ignoring" | Implies they are missing something important | | "We analyzed 10K emails. Here's what we found." | Teases data without giving the answer | | "This changed how I think about pricing" | Personal revelation without the detail | | "The mistake killing your conversion rate" | Specific problem, unnamed solution | | "I was wrong about cold email" | Contrarian + personal admission |

**Rules:**

• Do not be vague to the point of irrelevance ("You won't believe this!").
• The email body must deliver on the curiosity promise.
• Use sparingly; overuse trains subscribers to distrust.

2. Urgency

Create time pressure that motivates immediate action.

| Example | Type | |---------|------| | "Last day: 40% off ends at midnight" | Deadline | | "Only 12 spots left for the workshop" | Scarcity | | "Price increases tomorrow" | Price urgency | | "Your trial expires in 48 hours" | Expiration | | "Flash sale: 6 hours only" | Time-limited |

**Rules:**

• Urgency must be real. Fake urgency destroys trust permanently.
• Do not use urgency in every email. Reserve for genuine time-sensitive offers.
• Avoid all-caps urgency words (LAST CHANCE, HURRY).
• Pair with a specific deadline, not vague "soon" language.

3. Personalization

Use subscriber data to make the subject feel individually crafted.

| Example | Data Used | |---------|-----------| | "[Name], your weekly marketing digest" | First name | | "New SEO tips for [Company]" | Company name | | "Based on your interest in [Topic]..." | Behavioral data | | "Your [City] marketing event this Thursday" | Location | | "[Name], you left items in your cart" | Name + behavior |

**Rules:**

• Personalization boosts open rates by 10-20% on average.
• Do not overuse first names. If every email starts with "[Name]," it loses effect.
• Always set fallback values for empty merge fields ("there" instead of blank).
• Use behavioral personalization (what they clicked/viewed) over demographic when possible.

4. Question

Pose a question the reader wants answered.

| Example | Type | |---------|------| | "Are you making this SEO mistake?" | Self-diagnosis | | "What's your content strategy for Q2?" | Planning prompt | | "Ready to double your email list?" | Aspirational | | "Which pricing model is right for you?" | Choice | | "Can you write a landing page in 30 min?" | Challenge |

**Rules:**

• Questions should be answerable only by opening the email.
• Avoid yes/no questions where the answer is obvious.
• Rhetorical questions ("Want to make more money?") feel spammy.
• The best questions imply a knowledge gap the reader wants to close.

5. Number/Listicle

Include a specific number for concreteness and scannability.

| Example | Why It Works | |---------|-------------| | "7 email templates that convert" | Promise of a defined, scannable list | | "3 things I'd change about my launch" | Small number = quick read | | "We grew 247% in 90 days" | Specific result = credibility | | "5-minute fix for your homepage copy" | Number quantifies the effort | | "11 subject line formulas (steal these)" | Odd numbers outperform even |

**Rules:**

• Odd numbers (3, 5, 7, 9, 11) tend to outperform even numbers.
• Specific numbers (247%) outperform round numbers (250%).
• Use digits, not words ("7" not "seven") for visual impact in the inbox.
• Keep lists short for emails (3-9 items); save long lists for blog posts.

6. How-To

Promise a practical, actionable skill or outcome.

| Example | Structure | |---------|-----------| | "How to write emails that actually get replies" | How to [outcome] | | "How I got 1K subscribers in 30 days" | How I [result] in [timeframe] | | "How to fix your bounce rate in 10 minutes" | How to [fix problem] in [time] | | "How top founders write investor updates" | How [authority] [does thing] |

**Rules:**

• "How to" subjects set a learning expect