8 subject lines from your draft. One run. Ready to test.
Paste your post and get 4 proven angles — curiosity, benefit, specificity, contrarian — with 2 variants each, labeled so you can drop them straight into Substack's A/B tool.
$3.99
Works in Claude + ChatGPT
01Generates 8 subject lines in one pass: 2 curiosity, 2 benefit, 2 specificity, 2 contrarian — all labeled for testing
02Works from a rough draft, a topic sentence, or even an existing subject line you want to improve
03Each variant is written to the angle, not just reshuffled words — curiosity hooks withhold, benefit lines promise, contrarian lines push back
04Bundled angle-patterns guide flags weak phrasing and power words specific to each of the 4 approaches
05Covers the angles that account for most open rate variance — so you're testing real differences, not synonyms
What it does
Your subject line does more work than anything else you write that week. This skill takes whatever you've drafted — a full post, a paragraph summary, a single topic sentence — and returns 8 subject line variants sorted into four distinct angles: curiosity (withholds the payoff), benefit (front-loads the win), specificity (names the number or the detail), and contrarian (challenges the received wisdom). Two variants per angle, each labeled, each ready to paste into Substack's native A/B test or any ESP that supports split testing.
This isn't a synonym shuffler. The bundled `angle-patterns.md` resource bakes in phrase patterns, power words, and anti-patterns for each angle — so the curiosity variants actually withhold, the benefit variants lead with a concrete outcome, and the contrarian variants have a real point of view. If a line feels flat, you can ask for a deeper pull on any angle and the skill knows exactly what to fix.
For Substack writers, ConvertKit users, and anyone running a paid or free newsletter who's tired of agonizing over a single subject line for 20 minutes — this is the faster, more systematic way to test your way to better open rates.
Frequently asked
Does it just generate the 8 variants or does it also explain why each one works?
Both. Each variant is labeled with its angle, and if you ask, it'll break down the specific technique being used — what's being withheld, what outcome is named, what assumption the contrarian line is pushing against. Useful when you want to learn the pattern, not just grab the output.
My newsletter is pretty niche (sourdough, burnout for freelancers, B2B SaaS). Will the angles still hold up?
Yes — the 4 angles are frame-level, not topic-level. Curiosity, benefit, specificity, and contrarian work whether you're writing about bread hydration percentages or managing a creative block. The examples in the skill cover exactly that range.
Can't I just prompt Claude or ChatGPT myself and get the same thing?
You can get 8 lines. What you won't get is the bundled angle-patterns guide that's loaded at runtime — the phrase patterns, power words, and anti-patterns that keep the variants from collapsing into each other. That's what makes curiosity variants actually feel like curiosity variants instead of reworded benefit lines.
Does this work in Claude.ai, ChatGPT, or other tools?
This is a Claude skill, so it runs inside Claude.ai on a plan that supports Skills. It won't run natively in ChatGPT or other tools.
I already have a subject line I wrote. Can I just ask it to improve that instead of pasting a full draft?
Yes. Hand it your existing subject line and the topic, and it'll generate the 8 variants from there — treating your line as a starting signal for the angle work.
Install
After purchase you'll get a license key. Then:
$ npx skilltree-network login # paste your license key