Subject lines
A Claude skill that writes 5-10 subject line variations under 50 characters, grouped by approach, with preview text pairings and an A/B recommendation. For anyone sending email who needs inbox-ready lines, not filler.
What it does
Give it the email topic and audience. It gives you three things:
- Subject set. Five to ten lines, each with character count and a one-line rationale. Grouped by curiosity, value-forward, specificity, personalization, and direct.
- Preview pairings. Complementary preview text for the top two or three subjects. Preview never repeats the subject.
- A/B recommendation. Two lines to test, with the isolated variable stated clearly.
Works in: Claude (claude.ai Projects or the desktop app), Cursor
Rules inside the skill: under 50 characters, no all-caps, no fake urgency, no emoji unless you ask, no em dashes, no spam-trigger language without a real offer
Sample input / output
You give it
"Email is a restock of the navy trench. Audience is past buyers. Tone is warm and specific. No discount."
It produces
Subject set: 8 lines under 50 characters, grouped by approach
Preview pairs: complementary text for the top 3
A/B rec: curiosity vs specificity, variable isolated
How to install
- Subscribe below. The SKILL.md file link arrives in the first email.
- Download the file. Create a folder:
.claude/skills/margarita-subject-lines/ - Put
SKILL.mdinside that folder. - In Claude, start a new project and use "Add to project knowledge" to include the skill folder.
- Begin with: "Use the margarita-subject-lines skill" and paste the email topic.
Cursor users: place the folder at .agents/skills/margarita-subject-lines/.
Who it is for
- Anyone sending campaigns or flows who needs inbox-ready subject lines
- Founder who writes their own Klaviyo and wants a 3-second inbox test, not a brainstorm
- Email lead who wants an A/B pair with the variable named, not ten similar lines
It will not invent urgency. If there is no real deadline, it will not write one.