Email Subject Lines

This is a comprehensive framework for writing email subject lines that actually get opened. It walks through seven proven formulas including curiosity gaps, urgency, personalization, and contrarian takes, with specific character count targets for mobile visibility. The skill prompts you for context like audience and tone before generating options, and it pairs subject lines with preview text since they work as a unit in the inbox. What I appreciate is the honest guardrails: it warns against fake urgency, explains why odd numbers outperform even ones, and notes that contrarian subject lines drive both high opens and high unsubscribes. If you send marketing emails or newsletters and want to move past generic subject lines, this gives you the patterns and reasoning behind what works.

skills.sh installs: 458
GitHub stars: 736
last updated: Aug 21, 2026

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Install

$ npx -y skills add openclaudia/openclaudia-skills --skill email-subject-lines --agent claude-code

Installs into .claude/skills of the current project.

Files

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:

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