Email Subject Line Laboratory

Generates and tests email subject lines using proven psychological triggers, A/B test frameworks, and performance prediction.

Category: marketing Difficulty: beginner
Platforms: chatgpt claude
Tags: email marketing subject lines open rates A/B testing

Prompt Template

You are an email marketing copywriter who has tested 10,000+ subject lines. Generate subject lines:

**Email Purpose:** {{purpose: newsletter/promotion/welcome/re-engagement/announcement/transactional}}
**Topic/Offer:** {{topic}}
**Audience:** {{audience}}
**Brand Voice:** {{voice: professional/casual/witty/urgent/luxury}}
**Current Average Open Rate:** {{rate: if known}}

Generate:

**1. Subject Line Sets** (5 categories, 3 each = 15 total)

**Curiosity Gap:**
Lines that create an information gap the reader must open to close.

**Benefit-Driven:**
Lines that promise a specific, tangible outcome.

**Social Proof:**
Lines that leverage others' behavior or results.

**Urgency/Scarcity:**
Lines that create time pressure (without being spammy).

**Personalization:**
Lines using [First Name], behavior data, or segmentation.

**2. Subject Line Scoring**
Rate each on:
- Open-worthiness (1-10)
- Spam trigger risk (low/medium/high)
- Mobile display (fits in 40 chars? Y/N)
- Brand alignment (1-10)

**3. A/B Testing Plan**
- Which 2 subjects to test first (and why these specifically)
- Test duration recommendation
- Sample size per variant
- How to read results (open rate isn't everything — check clicks too)

**4. Preview Text Pairs**
For top 5 subject lines, write matching preview text (40-90 chars) that extends the hook rather than repeating it.

**5. Seasonal/Timing Notes**
Optimal send time for this email type and any day-of-week considerations.

Tips