write-a-skill

write-a-skill is a skill for Claude Code, Codex from OutlineDriven/odin-gemini-cli-extension. It costs 80 tokens per session (892 once invoked), scanned A, a copy of write-a-skill, Apache-2.0.

A guide for authoring one focused coding-agent skill with its instructions, supporting files, and usage boundaries.

In plain words
What is it for?
Use it when creating or refining a SKILL.md for a specific task, including its triggers, limits, examples, and tests.
Why use it?
It helps turn a capability into a consistent, reusable skill instead of an informal set of notes.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions AGENTS.md.

Good fit Use it when creating or refining a SKILL.md for a specific task, including its triggers, limits, examples, and tests.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/outlinedriven/odin-gemini-cli-extension/write-a-skill
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add OutlineDriven/odin-gemini-cli-extension --skill write-a-skill
Clone the repo
git clone --depth 1 https://github.com/OutlineDriven/odin-gemini-cli-extension

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 write-a-skill

README.md
[![agentmods](https://agentmods.dev/badge/skills/outlinedriven/odin-gemini-cli-extension/write-a-skill.svg)](https://agentmods.dev/skills/outlinedriven/odin-gemini-cli-extension/write-a-skill)
Your own site
<a href="https://agentmods.dev/skills/outlinedriven/odin-gemini-cli-extension/write-a-skill"><img src="https://agentmods.dev/badge/skills/outlinedriven/odin-gemini-cli-extension/write-a-skill.svg" alt="Measured on agentmods" height="20"></a>
Per session 80 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 892 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 97% copy Near-identical to another mod 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 $0.00080 $0.00892
Opus 5 $0.00040 $0.00446
Sonnet 5 $0.00016 $0.00178
Haiku 4.5 $0.00008 $0.00089

Measured 4d ago against content hash 58de79f4e94e, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

write-a-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 4d 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.

Origin

This is a copy

97% identical to write-a-skill — 1 line differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/skills/write-a-skill/SKILL.md · 83 lines

How it starts

The opening of the file, as written. The whole thing — 83 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill authoring loop: gather requirements, draft against the SKILL.md contract, review with the user, refine. One concern per skill; one skill per directory. Apply the skill-creator:skill-creator methodology (three-level progressive disclosure, pushy descriptions, evals.json).

Scope disambiguation

  • write-a-skill — authors one SKILL.md for one capability inside an existing skills tree.
  • Repo onboarding — onboards a whole repository, scaffolds AGENTS.md and project conventions.
  • skill-creator:skill-creator — the upstream methodology this skill applies; consult it for the canonical contract.

Authoring loop

  1. Gather requirements — surface decisions before drafting:

    • Capability boundary: what task does the skill cover, what does it explicitly not cover?
    • Trigger phrases: which user phrases or contexts should load it?
    • Determinism: any operation deterministic enough to live in a script rather than re-generated prose?
    • Bundled references: docs, schemas, or examples to include?
    • Static guarantee context: language family (Rust, TypeScript, Python, Kotlin, Go, OCaml, …) — affects testing-charter scope.
  2. Draft the SKILL.md — write to the contract below. Keep body terse and decision-oriented.

  3. Review with the user — present the draft, surface ambiguous decisions, and refine.

  4. Verify — run any bundled evals.json cases; targeted re-read of the SKILL.md to confirm description triggers and body alignment.

Directory layout

skill-name/
  SKILL.md              # contract; required
  references/           # deeper docs loaded on-demand
    REFERENCE.md
    EXAMPLES.md
  scripts/              # deterministic helpers
    helper.{ts,py,sh}
  evals.json            # trigger / behavior evals

Reference paths in SKILL.md use references/X.md, never ./X.md.

SKILL.md contract

---
name: skill-name
description: <what the skill does>. <when to trigger it — concrete phrases or contexts>.
---

<One-line imperative summary of the skill's posture.>

## <Section> — terse decision-oriented prose

<Body in imperative voice with brief why. ≤200 lines.>

Read the full file on GitHub · 83 lines

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. 4d ago First seen · 83 lines · 80 tokens per session scan A 58de79f4e94e

Subscribe to this mod's changes

write-a-skill is a skill published in the GitHub repository OutlineDriven/odin-gemini-cli-extension (5 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 80 tokens to every session and 892 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. It is 97% identical to write-a-skill, differing in 1 line, and is treated as a copy.

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