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Marketing skill for Claude with 26 evals – +20pp over baseline

A new marketing skill for Claude, built on a progressive disclosure architecture, achieved a mean pass rate of 82.7% across 26 evaluations, outperforming the baseline by 20.4 percentage points. The skill uses a lightweight routing layer to load nine specialist playbooks only when relevant, avoiding context bloat while delivering specialist-level copywriting, brand messaging, and competitive analysis. It works across Claude Code, Claude.ai, the Claude API, Cursor, Codex CLI, and Gemini CLI, and is available as an open-source install.

read10 min publishedMay 30, 2026

Unlike single-file marketing prompts, this skill uses progressive disclosure: a lightweight routing layer (SKILL.md

) that loads 9 purpose-built reference modules only when relevant. The depth of nine specialist playbooks, none of the context bloat. Works with Claude Code, Claude.ai, the Claude API, Cursor, Codex CLI, Gemini CLI, and anything that reads the open SKILL.md

format.

Before / AfterBenchmarksInstallWhat you getUse casesHow it worksThe brief-first philosophyThe universal quality barEvaluationDesign principlesFAQRoadmapContributingLicense

Prompt: "I need words for the top of my homepage — it's a tool that schedules social posts."

❌ Without the skill ✅ With the skill
"Welcome to the future of social media management! Our powerful, all-in-one platform helps you streamline your workflow and supercharge your presence."
Assuming small businesses / solo creators managing their own social presence — adjust if you mean agencies.Headline: Schedule a week of social posts in 20 minutes.Subhead: Plan, schedule, and publish across every channel — so you show up consistently without living on your phone.CTA: Start scheduling free
Vague adjectives, no audience, no CTA, says nothing only-this-product could say. Outcome-led headline, real subhead + CTA, one stated assumption, sharpening questions offered after the draft.

That difference is measurable — see below.

Each of 26 eval prompts was run with the skill and without it (baseline), then graded against per-prompt assertions. Full method, per-eval table, and raw outputs in benchmarks/ and

.

evals/

Metric With skill Baseline Delta
Mean pass rate
82.7%
62.3% +20.4 pp
Evals where skill ≥ baseline 23 / 26
Gates (A & B) + negative controls ✅ correct n/a

Where it moves the needle most:

Eval With Base Why
positioning statement (Gate A) 1.00 0.00 asks the load-bearing questions instead of guessing
honesty probe 1.00 0.25 placeholders, never fabricated testimonials/stats
homepage hero 1.00 0.25 drafts outcome-led copy on a stated assumption
competitor analysis 1.00 0.33 ends in a white-space gap, not just description
pricing-page audit (Gate B) 1.00 0.67 demands the real asset before auditing
cold email 0.86 0.43 one idea, one low-friction CTA, relevance-first

Negative controls ("name my cat", "explain DNS", "thank-you note to grandma") correctly did not trigger the skill — no false positives. A few weak spots (welcome-sequence, LinkedIn) are tracked openly in benchmarks/README.md.

📊 Browse every output and grade: open evals/review.html in a browser.

curl -fsSL https://raw.githubusercontent.com/inerrata/marketing-tool/main/install.sh | bash

irm https://raw.githubusercontent.com/inerrata/marketing-tool/main/install.ps1 | iex

### Claude Code (project-specific)

``` bash
cp -r marketing-tool/_unpacked/marketing .claude/skills/marketing

Download marketing.skill

and upload it under Settings → Capabilities → Skills (Pro/Max/Team/Enterprise). The file is just a zip of _unpacked/marketing/

— repackage it yourself with any zip tool.

Module Covers
Copywriting
Ads, emails, landing/sales pages, homepages, CTAs, taglines, social posts, microcopy — PAS / AIDA / BAB / 4Ps / FAB, 10-point editing checklist
Brand & messaging
Positioning, value propositions, messaging hierarchy, brand voice & tone, naming, message testing
Content strategy
Content pillars, funnel mapping, calendars, content ratios, repurposing, distribution, audits
Campaigns & GTM
Campaign briefs, concept development, phased launches, go-to-market plans, asset checklists
Research
Personas, ICPs, segmentation, jobs-to-be-done, competitor gap analysis, voice-of-customer
SEO
Search intent, keyword strategy, content briefs, on-page optimization, E-E-A-T
Email & lifecycle
Welcome / nurture / sales / onboarding / win-back / abandoned-cart sequences, newsletters, deliverability
CRO
Conversion audits, the conversion equation, A/B testing methodology, high-impact fixes
Measurement
Metrics by goal, AARRR funnel, CAC / LTV / ROAS formulas, attribution, reporting

Concrete scenarios, the prompt that triggers them, and what you get back.

You want to… Say… You get
Launch a product with no plan "Help me launch my habit-tracking app."
Scoping questions, then a one-page brief + phased pre-/launch/post timeline + asset checklist
First customers from zero "Nobody knows my store exists. How do I get my first 100 customers?"
A focused acquisition plan — one channel/motion to start, matched to audience
GTM as a solo founder "Launching a paid Notion-template business next month, no audience — what's my plan?"
A sequenced GTM plan (research + channel + content + email + launch), one motion first
You want to… Say… You get
Cold outreach email "Cold email to SaaS founders for my churn-reduction tool."
Subject + preview, relevance-first opening, one idea, one low-friction CTA
Homepage hero "Words for the top of my homepage — a tool that schedules social posts."
Headline + subhead + CTA options, outcome-led, on a stated assumption
Subject-line options "3 Black Friday subject lines for a coffee subscription."
Three distinct angles (curiosity / benefit / urgency), labeled, length-checked
Avoid fake proof "Write a landing page with impressive testimonials and stats."
The page, with marked placeholders + why fabricating proof breaks trust and law
You want to… Say… You get
Nail positioning "Positioning statement for a PM tool aimed at agencies."
2–3 sharp questions first, then a defensible statement — not a guess
Define brand voice "Help me define my brand voice."
Short discovery, then a voice profile with do/don't dimensions and tone-by-moment
Value proposition "Meal-prep for busy parents, ready in 5 min, no ultra-processed — write my value prop."
An outcome-led value prop only your brand could say
You want to… Say… You get
Content calendar "Content calendar for a B2B fintech startup."
3–5 pillars, funnel mapping, value-heavy mix, calendar w/ pillar/stage/format/title/CTA
SEO brief "SEO brief targeting 'best crm for nonprofits'."
Intent → format, title/meta, outline, People-Also-Ask, E-E-A-T, with a real-data flag
Welcome sequence "Design a welcome sequence for my newsletter."
3–5 email flow with timing + one CTA each
Win-back "Win-back sequence for users inactive 60 days."
Re-engagement flow + suppression of non-responders to protect deliverability
Audit a page "My pricing page isn't converting — audit it."
Asks for the real page first, then a structured audit + prioritized fixes
What to measure "What should I track for a new paid ads channel?"
Primary metric (CAC/ROAS), leading indicators, formulas, vanity-metric + attribution caveats
Unit economics "Is a $400 CAC good if customers pay $50/mo for ~18 months?"
LTV + LTV:CAC math shown, read against ~3:1, with the caveats
marketing/
├── SKILL.md              ← routing layer, brief-first gates, quality bar
└── references/
    ├── copywriting.md      ├── research.md         ├── email-lifecycle.md
    ├── brand-messaging.md  ├── seo.md              ├── cro.md
    ├── content-strategy.md ├── campaigns.md        └── measurement.md

At session start, only the SKILL.md

description (~100 tokens) is in context. When a marketing task is detected, the full SKILL.md

loads and routes to the relevant module(s); unused modules never load. Multi-area requests pull several and synthesize.

Two hard gates enforce quality:

Gate A — Strategy foundations(positioning, value prop, voice, GTM): asks 2–3 sharp questions before writing. These are load-bearing — everything downstream inherits their flaws.Gate B — Audits / "improve my X": requests the actual asset first. It won't invent a page's contents and critique its own invention.

Everything else scales to stakes: big ambiguous strategy work gets a couple of questions first; a concrete copy deliverable (a hero, an ad, subject lines) is drafted immediately on a stated assumption, with sharpening questions after — a draft you can react to beats an interrogation.

Before producing anything, the skill establishes (or explicitly infers and flags) five things:

Audience— who specifically, and what do they believe now?** Goal**— the one action this should drive.** Offer**— what's marketed, and the single most important thing about it.** Proof**— the evidence behind the claims.** Constraint**— channel, length, tone, brand rules.

Audience and goal are never silently guessed. When the skill assumes, it says so ("Assuming [X]; adjust if wrong") so you can correct it in one line.

Checked against every deliverable before it ships: specificity (numbers, not adjectives) · reader-first · one message per piece · proof over claims · clean mechanics (active voice, cut filler) · earn the next line · honesty (no fabricated stats, testimonials, or credentials).

The skill ships with its own test suite in evals/:

26 prompts covering every module, phrasing variations, both gate checks, multi-module synthesis, an implicit trigger, an honesty probe, and

negative controls(prompts that should

nottrigger it).

The harness runs each prompt with and without the skill, records whether the skill chose to trigger (available, not forced), and grades every output against per-prompt assertions — measuring triggering accuracy and output quality at once.

  • 📊 Aggregate + per-eval table → benchmarks/README.md

  • 🧪 Eval set + harness + raw results → evals/

  • 🖥️ Click-through viewer → evals/review.html

Reproduce it in Claude Code with the skill-creator

skill:

Use the skill-creator skill to run a full eval pass on ./_unpacked/marketing using ./evals/evals.json.
Run with-skill and baseline for each prompt, grade against expected_output, and generate the benchmark viewer.

Specificity over cleverness— numbers and outcomes, not vague adjectives** Reader-first**— leads with the audience's problem, not the product's features** Brief before output**— never silently guesses on audience or goal** Proof over claims**— every significant claim needs support** One message per piece**— every asset has exactly one job** Draft-first for copy, questions-first for strategy**— match friction to stakes** Honest by default**— never fabricates proof; surfaces advertising/email-compliance considerations

Does it need an API key or dependencies? No — plain Markdown in the SKILL.md

format. Nothing to run or install.

Why does it sometimes ask questions instead of answering? For strategy foundations and audits, a confident guess is worse than a question. For ordinary copy, it drafts first and asks after.

Will it invent testimonials or stats if I ask? No. It uses marked placeholders and explains why fabricated proof breaks trust and advertising law.

Does it work outside Claude? Yes — any tool that reads SKILL.md

(Cursor, Codex CLI, Gemini CLI, …).

How is this different from "be a marketer"? Frameworks, gates, and a quality bar make output consistent and grounded — and the eval suite lets you verify it instead of trusting vibes.

Can I customize it? Yes — edit the reference modules for your brand rules/voice, and add eval prompts to keep it honest.

  • More reference modules (paid-media buying, partnerships/influencer, PR & comms, localization)
  • A brand-profile file the skill reads so output inherits your voice automatically
  • Multi-run (3×) eval pass with variance reporting; fix the tracked weak spots (#15, #8)
  • More worked before/after examples

Star if useful.

PRs and issues welcome.

  • Keep SKILL.md

lean — it's always loaded; depth goes inreferences/

  • Add eval prompts in evals/evals.json

for any new module (happy path + a phrasing variation + gates) - Run the eval set before and after your change so triggering and quality don't regress

MIT — see LICENSE.

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