1. Subject Line Prompts That Generate Actual Opens
Subject lines are where most AI-assisted email work collapses. The model defaults to curiosity-gap clickbait because that's what the training data is full of. The fix is specificity: give the model your audience, the single thing you want them to feel, and constraints that prevent lazy patterns.
**Prompt — Batch subject line generation:** ``` You are a senior email copywriter. Generate 10 subject lines for an email to [AUDIENCE — e.g., "SaaS founders on a free trial"] about [TOPIC — e.g., "upgrading before their trial ends"]. Constraints: - Each subject line under 50 characters - No question marks - No "Here's how" or "Don't miss" openers - Mix of angles: urgency (2), social proof (2), curiosity (2), benefit-first (2), conversational (2) - Brand tone: [TONE — e.g., "direct, no hype, founder-to-founder"] For each subject line, add a one-sentence note on why it works and which segment it targets best. ```
**Why it works:** The angle constraint forces the model to produce genuinely different options rather than variations on a single approach. The character limit prevents the lazy long-form subject line that performs well in prompts but poorly in inboxes. The one-sentence annotation makes the batch useful as a briefing document, not just a pick-one list.
**Prompt — Single subject line with pre-header:** ``` Write a subject line + preview text pair for this email: Email purpose: [PURPOSE — e.g., "announce a 48-hour sale on annual plans"] Audience: [AUDIENCE — e.g., "monthly subscribers who have been active for 90+ days"] One feeling to create: [FEELING — e.g., "relief — they've been thinking about upgrading and this makes the decision easy"] Brand voice: [VOICE — e.g., "warm, honest, never salesy"] Format: Subject: [subject line, under 45 chars] Preview: [preview text, 85-100 chars, continues the thought from the subject — do not just summarize the subject] ```
GPT-5 and Claude Opus 4.8 both perform well here. Claude tends to avoid superlatives and hype language by default — useful for B2B. GPT-5 leans slightly more conversational, which works better for DTC and consumer newsletters.