# Marketing skill for Claude with 26 evals – +20pp over baseline > Source: > Published: 2026-05-30 19:36:46+00:00 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 / After](#before--after)[Benchmarks](#benchmarks)[Install](#install)[What you get](#what-you-get)[Use cases](#use-cases)[How it works](#how-it-works)[The brief-first philosophy](#the-brief-first-philosophy)[The universal quality bar](#the-universal-quality-bar)[Evaluation](#evaluation)[Design principles](#design-principles)[FAQ](#faq)[Roadmap](#roadmap)[Contributing](#contributing)[License](#license) **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/](/inerrata/brief/blob/main/benchmarks) and [.](/inerrata/brief/blob/main/evals) `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](/inerrata/brief/blob/main/benchmarks/README.md). 📊 **Browse every output and grade:** open [ evals/review.html](/inerrata/brief/blob/main/evals/review.html) in a browser. ``` # macOS / Linux curl -fsSL https://raw.githubusercontent.com/inerrata/marketing-tool/main/install.sh | bash # Windows (PowerShell) 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/](/inerrata/brief/blob/main/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 *not*trigger 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 in`references/` - 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](/inerrata/brief/blob/main/LICENSE).