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

Source material given with the request

Tool: Inboxcheck. You send one test email to an address we give you; within 2 minutes you get a report on spam-filter results at Gmail, Outlook and Yahoo, plus SPF, DKIM and DMARC setup. Free, 3 checks per day, email address required.
with the skill
*A: This is a fresh page with a clear offer. Lead with the test results, explain the one-email process, and make the free limit visible.* ## Signup page copy ### Check your email for spam issues before you send Send one test email to Inboxcheck. Within 2 minutes, get spam-filter results for Gmail, Outlook and Yahoo, plus checks of your SPF, DKIM and DMARC setup. **Email address** Placeholder: you@company.com **[Get my test email address]** Free · 3 checks per day ### One test email. A report in 2 minutes. 1. **Get your test address** Enter your email address, and we’ll give you an address to send your test to.
Show the rest (24 more lines)
2. **Send the email you want to check** Send it to that address from the account you plan to use. 3. **Review your results** See spam-filter results for Gmail, Outlook and Yahoo. Check whether your email authentication is set up correctly with SPF, DKIM and DMARC results. *Test results help flag potential problems. They don’t guarantee inbox placement for every recipient.* --- ## Copy notes - **The headline promises a check, not guaranteed delivery.** That keeps the offer credible. - **The CTA names the next step.** The free allowance sits beside it so visitors know what they’re getting before entering their email. ## Alternatives **Headlines** - **How will spam filters treat your email?** Leads with the visitor’s question. - **Get a spam-check report from one test email** Emphasizes the small amount of work required. **CTAs** - **Get my Inboxcheck test address** Adds the product name. - **Start my free email check** Emphasizes the free offer.
without
# Check your email before you hit send Will your email land in spam? Test it with Inboxcheck and get spam-filter results for Gmail, Outlook and Yahoo—plus checks on your SPF, DKIM and DMARC setup. **Get your report within 2 minutes of sending a test email.** ### Start your free check **Email address** *you@company.com* **[Get my test address]** Free · 3 checks per day ### One test email. A clearer picture. 1. **Get your test address** Enter your email to get a test address from Inboxcheck.
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2. **Send your test email** Send the email you want to check to that address. 3. **See your results** Review spam-filter results and email authentication checks in one report. *A test gives you a snapshot—not a guarantee of inbox placement for every recipient.*

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.