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skills / marketing

copywriting

what it does

When the user wants to write, rewrite, or improve marketing copy for any page, including homepage, landing pages, pricing pages, feature pages, about pages, or product pages. Also use when the user says "write copy for," "improve this copy," "rewrite this page," "marketing copy," "headline help," "CTA copy," "value proposition," "tagline," "hero section copy," "this copy is weak," "this sounds like AI," "AI slop," "make it sound human," or "help me describe my product." Drafts never use AI tells like "it's not X, it's Y" reveals, "no X, no Y, no Z" lists, or sentences that trail into extra comma clauses. For email copy, see emails. For popup copy, see popups. For editing existing copy, see copy-editing. For the offer underneath the copy (bonuses, guarantees, value framing), see offers. Claims must be supportable, and a declined claim names the evidence that would unlock it. Diagnoses the input first (blank brief, real voice, or point edit) and changes only what it calls for.

by Corey Haines · Corey Haines, MIT · version 1 · license MIT

Verified Before and after: 2 models 1 try per case View source Download .zip

Compare the answers

Answers from Claude Sonnet 5.5 and GPT-6.1 Sol · try 1 of 1

Same request, same model, once with the skill and once without. Read both and judge for yourself.

“Write a 'Why teams switch' section for Ledgerline's homepage, about 120 words.”

Source material given with the request

Ledgerline is bookkeeping software for agencies of 5 to 50 people. Customer survey, Jan 2026 (85 agencies): month-end close took 38% less time after switching. Connects to Stripe, Gusto and three US banks. Exports to QuickBooks. Customers named in public: none.
with the skill
**Diagnosis:** A. The brief is facts only, with no draft or voice to preserve. I built the section around the one hard proof point (the 38%) and kept every other claim to what you listed. ## Section copy **Month-end close takes 38% less time** In our January 2026 survey of 85 agencies, customers reported that month-end close took 38% less time after they switched to Ledgerline. Month-end is when payments, payroll, and bank activity all have to agree. Stripe payments and Gusto payroll sync into Ledgerline, and it pulls transactions from three US banks, so you reconcile in one place. If your accountant works in QuickBooks, Ledgerline exports to it. It's built for agencies of 5 to 50 people. **CTA:** See how Ledgerline fits your agency ## Notes - **Length:** This runs about 90 words, not 120. Reaching 120 would mean inventing detail about what customers switched from or how the product works. The `[NEED]` items below would fill the gap with real material. - **Headline:** It leads with the stat because it's the only specific, falsifiable claim available, and it passes the "Now you can" test. - **Survey wording:** I wrote "customers reported" because it's a survey, so the figure is self-reported. I didn't write "average," "faster," or "guaranteed," and I didn't claim the integrations cause the 38%. The survey doesn't show that.
Show the rest (7 more lines)
## Needed to strengthen it - `[NEED: social proof]` Customers can't be named, so a testimonial would have to be anonymous with role and agency size, e.g. "Operations lead, 22-person design agency". That requires a real quote with the customer's permission. - `[NEED: survey details]` Is 38% the average or median, and did agencies report close time before and after? If so, I can write "from X days to Y," which is more concrete than a percentage. - `[NEED: bank names]` Naming the three banks passes the swap test far better than "three US banks." - `[NEED: switched from what]` The heading says "switch," but I don't know what teams leave (spreadsheets, QuickBooks, a bookkeeper?). If the survey asked, that's the strongest angle for this section. - `[NEED: CTA destination]` Is it a trial, a demo, or a pricing page? The button text should match.
without
## Why teams switch **Close the month faster.** In our January 2026 survey of 85 agencies, month-end close took 38% less time after switching to Ledgerline. Less chasing, less reconciling, more time for client work. **Connect the tools you already use.** Ledgerline syncs with Stripe and Gusto, plus three major US banks, so revenue, payroll, and transactions land in one place without manual entry. **Keep your accountant happy.** Export to QuickBooks whenever you need to. Your accountant keeps working in the system they know, and you skip the spreadsheet handoffs. **Built for agencies of 5 to 50.** Ledgerline is designed for growing agencies, not solo freelancers or enterprise finance departments. --- *Word count: about 120. I left out customer names and quotes since none are public. If you later get permission to name a customer, a short testimonial would fit well after the first block. Also consider naming the three banks if you're comfortable doing so, since that specificity helps visitors check compatibility.*

Answers are shown exactly as the model wrote them, from the first try, and nothing is picked by hand.

The models

2 models

Claude Sonnet 5.5

made by Anthropic

claude-sonnet-5-5 · revision not reported by the provider

1 try per case · tested 1 Nov 2026

GPT-6.1 Sol

made by OpenAI

gpt-6.1-sol · revision not reported by the provider

1 try per case · tested 1 Nov 2026

The tasks

Our tests

feature-section

“Write a short feature section for Pinpoint's new scheduled reports feature.”

hero-invoicing

“Write the hero section for Tallybook's homepage: headline, subheadline and button text.”

rewrite-headline

“Rewrite this headline: 'An Innovative AI-Powered Platform for Streamlined Business Operations'. It's for a tool that helps small businesses send invoices and collect payments.”

signup-page

“Write the copy for the signup page of our free tool that checks whether your email will land in spam.”

why-switch-section

“Write a 'Why teams switch' section for Ledgerline's homepage, about 120 words.”

The creator’s own tests

creator-1

“Write homepage copy for a SaaS tool that automates employee onboarding. Target audience is HR directors at mid-size companies (200-2000 employees). Main differentiator is that it integrates with all major HRIS systems and cuts onboarding time from 2 weeks to 2 days.”

creator-10

“Can you make this homepage hero better? I wrote it myself and it feels rough. Headline: Your agency doesn't need another dashboard. It needs to get paid. Subhead: We got sick of chasing clients for money, so we built the thing that does it for us. Invoices go out when the work ships. Late payers get nagged. You get your evenings back. CTA: Try it free”

creator-2

“Rewrite this headline: 'An Innovative AI-Powered Platform for Streamlined Business Operations' — it's for a B2B SaaS tool that helps small businesses manage invoicing and payments.”

creator-3

“i need copy for my pricing page. we have three plans: starter ($29/mo), pro ($79/mo), business ($199/mo). it's a social media scheduling tool for marketers”

creator-4

“Write copy for our About page. We're a 3-person startup that built a developer tool for database migrations. Founded because we kept losing data during migrations at our last jobs. Tone should be professional but human.”

creator-5

“Can you improve this CTA? We currently have 'Learn More' on our feature page for our analytics dashboard product.”

creator-6

“Write me a 5-email welcome sequence for new trial users of our project management tool.”

creator-7

“Review this copy and tell me what's wrong: 'We are extremely excited to announce our revolutionary, cutting-edge platform that will totally transform how businesses optimize their workflows! Sign up now!!'”

creator-8

“Write above-the-fold copy for a calendar scheduling tool. Our differentiator is that the recipient gets to overlay their own calendar on the invite, so picking a time feels fair to both people instead of one-sided. Same product needs to work for indie founders AND for enterprise ops teams.”

creator-9

“Write a homepage hero (headline, subhead, CTA) and a short launch post for X for our Shopify inventory app. It installs from the Shopify App Store in one click, needs no signup form or credit card, and runs low-stock alerts, reorder emails, and supplier purchase orders off the product and sales data the store already has, so there's nothing to import.”

Install

Download the .zip and unzip it. Put its files, in a folder named copywriting, here:

Claude Code~/.claude/skills/Every project. For one project only, use .claude/skills/ inside it.
Codex~/.agents/skills/Every project. For one repository only, use .agents/skills/ inside it.
Cursor~/.cursor/skills/Cursor also reads the Claude Code and Codex folders above.

Then start a new session and ask for what the skill does. Other agents that read SKILL.md have their own skills folder; check their docs.

Coming after launch: get skills from inside your agent, no download needed.