A guided process for creating a new coding-agent skill from the ground up, including its activation examples and checks that it follows the required format.

It helps scaffold a new skill, collect its required details, register when it should activate, and run checks before it is added.

It helps avoid missing files, naming rules, trigger patterns, or validation steps when adding a skill to a project.

write-skill — Command by iliaal

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.

agentmods

npx agentmods add commands/iliaal/whetstone/write-skill

Clone the repo

git clone --depth 1 https://github.com/iliaal/whetstone

Made for: Claude Code.

Per session 41 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 3,146 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

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.

Model	Per session	Once invoked
Fable 5	$0.00041	$0.03146
Opus 5	$0.00020	$0.01573
Sonnet 5	$0.00008	$0.00629
Haiku 4.5	$0.00004	$0.00315

Measured 2d ago against content hash 4a8b97b20fc5, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

write-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 2d 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.

.claude/commands/write-skill.md · 226 lines

How it starts

The opening of the file, as written. The whole thing — 226 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Write Skill

Skill name: $ARGUMENTS

Scaffold a new plugin skill from scratch, generate paired trigger fixtures, register the regex pattern, and run all gates. For distilling a skill from skills.sh sources, use the skill-distiller skill instead — /write-skill is for skills with no external upstream.

Phase 1: Resolve target

If $ARGUMENTS is empty or doesn't start with ia-, ask for the skill name.
Validate format: must match ^ia-[a-z0-9][a-z0-9-]*$, no consecutive hyphens, no banned tokens (anthropic, claude).
Confirm the skill doesn't already exist:
- plugins/whetstone/skills/<name>/SKILL.md must NOT exist.
- distillery/tests/fixtures/triggers/<name>.jsonl must NOT exist.
- No matching SKILL_PATTERNS[<name>]= line in plugins/whetstone/hooks/skill-patterns.sh.
Read CLAUDE.md "Skill compliance checklist" section to refresh the gates this skill must pass.

Phase 2: Batch up-front interview

Use AskUserQuestion once to collect everything needed before scaffolding. Do not drip-feed questions across turns.

Ask:

Class — one of the five values from CLAUDE.md "Skill class taxonomy": language, discipline, workflow, meta, tool. Read that section before asking so the option descriptions match what the validator will accept.
Scope summary — one or two sentences: what this skill is for, when it fires.
Primary trigger vocabulary — 3-6 distinctive phrases users would type.
Existing skills it should not overlap with — names of any close-in-scope ia-* skills the user already has in mind.

Phase 3: Inspect prior art

Read the SKILL.md of every skill the user named in question 4 (and any others that look similar by class). Goals:

Match house style (frontmatter shape, body voice, references/ patterns).
Identify trigger overlap risk — validate-plugin will flag descriptions with >70% word overlap.
Find a close structural template to model the new skill after.

Phase 4: Scaffold

Read the full file on GitHub · 226 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.

2d ago First seen · 226 lines · 41 tokens per session scan A 4a8b97b20fc5

Subscribe to this mod's changes

write-skill is a command published in the GitHub repository iliaal/whetstone (32 stars, last pushed 3d ago), licensed MIT. It adds 41 tokens to every session and 3,146 once invoked, about $0.0002 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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