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.
curl -O https://raw.githubusercontent.com/briancl2/CustomerNewsletter/main/.github/skills/building-skill/SKILL.mdgit clone --depth 1 https://github.com/briancl2/CustomerNewsletterWrote 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.
[](https://agentmods.dev/skills/briancl2/customernewsletter/building-skill)<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.
<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>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.
| Model | Per session | Once 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 |
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.
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.
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
- Primary Purpose: "What should this skill help accomplish?"
- Trigger Scenarios: "What would a user say or do that should activate this skill?"
- 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:
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.
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.
- 9d ago First seen · 495 lines · 92 tokens per session scan A 4e717a639dd9
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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