BINGLEY
Sully Fazie

Cold Email Builder

5 mins

A skill that writes your cold email, or rebuilds the one you've got, then scores it against real reply data. Not a random AI generator.

Before you start

If you don't have the Claude desktop app, you'll need it first, so download it here.

Download for Mac Download for Windows

(You'll also need Claude Pro, around $20. Nothing else to sign up for.)

Part 1 · Claude Cowork setup(4 mins)
1

Install Cowork

Download the Claude desktop app and sign in on a paid plan. It has to be the desktop app, not the browser, because that is the version that can read your files and connect to your tools.

2

Open Cowork and give it a folder

Cowork is where Claude actually does work on your computer, not just chat. Get in and point it at one folder:

  • Open the desktop app and switch to Cowork, the middle of the three modes at the top.
  • Click New Task, then Work in a Project, then Choose a folder.
  • Make a fresh, empty folder (I call mine Claude Playground).

Claude only ever sees that one folder, nothing else on your computer, and it uses it to save your drafts and scores. So it stays private and tidy.

Part 2 · Cold Email Builder setup(1 min)
1

Install the skill

A skill is a saved set of instructions Claude follows every time. You install it once, then it's yours.

Download the skill
  • It saves a small file, cold-email-builder.skill, to your Downloads.
  • In a new Cowork task, drag the file into the chat, then click the Save skill button that appears on it.
  • Check it worked: click + at the bottom of the chat, then Skills. You should see it listed.

You only do this once. No other accounts, no connectors, nothing to pay for.

2

Run it

Two ways to use it. Score one you already have, or have it write you a fresh one.

  • Open a New Task and click + > Skills > cold-email-builder.
  • To grade: paste a cold email and ask it to score it.
  • To build: tell it who you're emailing and what you sell.
  • Either way it asks four quick questions first so the score is honest.

You get a band out of 100, the gates it passed or failed, the two or three changes that move the score most, and a rewrite, re-graded so you can see the lift. Use it on every email before you send.

Before you finish (quick checks)

New How was this skill built? (Click here) ▾

How was this skill built?

Every skill ships only after planning, research, building, testing and re-testing. Here is the record for the cold email builder.

10 calibration runs 94% inter-rater agreement 92-email stress run
PlanningMapped the two modes, build and grade, onto one shared rubric, and the intake that keeps every score honest, before writing a line.
Research & background checksBuilt an evidence base from published large-sample reply-rate studies, then tore down the market leaders, Lavender and Regie, for what actually moves replies.
BuildOne evidence-calibrated rubric used both to write and to grade, so the two never drift apart. Every judgement carries a traceable evidence tag, not a vibe.
Testing & re-testingCalibrated across 10 runs at 94% blind inter-rater agreement, a 92-email volume run with zero crashes, and live before-and-after rebuilds.
OrganisationVersioned scoring model with an outcomes log that records real sent-email results, so it keeps calibrating against reality.

    Key strengths

  • ✓Builds or rebuilds, then grades on the same rubric, so the writing and the critique always agree.
  • ✓Every score is tagged to a real source, not a generic AI guess.
  • ✓Honest by design: it won't fake proof or personalisation, and tells you when a template caps the grade.
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Sully Fazie
By Sully Fazie
sullyfazie.com