CustomerNewsletter: Skill for Claude Code

.github/skills/building-skill/SKILL.md

building-skill is a skill for Claude Code, Codex from briancl2/CustomerNewsletter. It costs 92 tokens per session (3,068 once invoked), scanned A, original, MIT.

A workflow for creating reusable Agent Skills: packages of instructions and supporting files that guide a coding agent through specialized tasks.

In plain words
What is it for?
Use it to plan, generate, test, validate, and package a new skill with files such as SKILL.md, scripts, references, assets, and examples.
Why use it?
It turns a set of user requirements into a structured skill package instead of leaving the instructions, scripts, tests, and reference material scattered.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

This is briancl2/CustomerNewsletter's own configuration. It tells Claude Code and Codex how to work on CustomerNewsletter itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything CustomerNewsletter configures →

Reuse

Borrowing it

Nothing to install: this file belongs to briancl2/CustomerNewsletter. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/briancl2/CustomerNewsletter/main/.github/skills/building-skill/SKILL.md
Clone the repo
git clone --depth 1 https://github.com/briancl2/CustomerNewsletter

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for building-skill

README.md
[![agentmods](https://agentmods.dev/badge/skills/briancl2/customernewsletter/building-skill/github.svg)](https://agentmods.dev/skills/briancl2/customernewsletter/building-skill)
Your own site
<a href="https://agentmods.dev/skills/briancl2/customernewsletter/building-skill"><img src="https://agentmods.dev/badge/skills/briancl2/customernewsletter/building-skill/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for building-skill

Your own site · 80×15
<a href="https://agentmods.dev/skills/briancl2/customernewsletter/building-skill"><img src="https://agentmods.dev/badge/skills/briancl2/customernewsletter/building-skill.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 92 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,068 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00092 $0.03068
Opus 5 $0.00046 $0.01534
Sonnet 5 $0.00018 $0.00614
Haiku 4.5 $0.00009 $0.00307

Measured 9d ago against content hash 4e717a639dd9, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

building-skill scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/validate_skill.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.github/skills/building-skill/SKILL.md · 495 lines

How it starts

The opening of the file, as written. The whole thing — 495 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill Builder

Create complete, production-ready Agent Skills from natural language descriptions. This skill guides you through understanding requirements, planning structure, and generating all necessary files.

What This Skill Produces

A complete skill package ready for distribution:

skill-name/
├── SKILL.md              # Core instructions + metadata
├── scripts/              # Executable automation (Python, Bash)
├── references/           # Documentation loaded into context as needed
├── assets/              # Templates, icons, boilerplate (used in output)
└── examples/            # Input/output examples for testing

Workflow Overview

flowchart LR
    A[Gather Requirements] --> B[Plan Skill Structure]
    B --> C[Generate Core SKILL.md]
    C --> D[Create Bundled Resources]
    D --> E[Generate Test Cases]
    E --> F[Validate & Package]

Step 1: Gather Requirements

Ask targeted questions to understand the skill's purpose. Avoid overwhelming—start with essentials:

Required Information

  1. Primary Purpose: "What should this skill help accomplish?"
  2. Trigger Scenarios: "What would a user say or do that should activate this skill?"
  3. Concrete Examples: "Give me 2-3 specific examples of how you'd use this skill."

Contextual Questions (as needed)

  • Input/Output Format: "What input does the skill receive? What should it produce?"
  • Degree of Freedom: "Should the output be strictly formatted or flexible?"
  • External Dependencies: "Does this require specific tools, APIs, or file types?"
  • Domain Knowledge: "Is there specialized knowledge the skill needs?"

Conclude Step 1 When

You can describe:

  • 3+ concrete usage examples
  • Clear trigger conditions
  • Expected input/output patterns
  • Any special requirements or constraints

Step 2: Plan Skill Structure

Analyze each concrete example to determine what reusable resources to include.

Decision Framework

For each example, ask:

Read the full file on GitHub · 495 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 9d ago First seen · 495 lines · 92 tokens per session scan A 4e717a639dd9

Subscribe to this mod's changes

building-skill is a skill published in the GitHub repository briancl2/CustomerNewsletter (11 stars, last pushed 3mo ago), licensed MIT. It adds 92 tokens to every session and 3,068 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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