skill-writing

argument-hint	<skill-name>
disable-model-invocation	false
name	skill-writing
user-invocable	true
description	Use to create/scaffold/init a new agent skill under `.agents/skills` in the working directory where invoked.

Skill Writing

Bootstrap a skill with a small observable contract, then symlink it into .claude/skills/ so Claude Code can discover it. Keep invariant workflow guidance in SKILL.md; move deterministic mechanics and conditional detail into scripts and references.

Model Optimization

Optimize every new skill and its content for GPT-5.6 and Claude Fable 5. The summaries below are reminders, not substitutes for the live guides. Read both guides before designing or writing a complex, long-running, multi-tool, or orchestration-heavy skill because their recommendations may evolve.

• GPT-5.6 prompting guidance: Prefer lean, outcome-first prompts that specify the goal, success and stopping criteria, constraints, evidence, permission boundaries, tool routing, output shape, and validation. Remove redundant scaffolding and evaluate changes on representative tasks.
• Claude Fable 5 prompting guidance: Use concise instructions that explain intent and boundaries; avoid over-prescription and scope creep; tune effort deliberately; ground progress claims in tool evidence; and make long-run verification and scaffolding explicit when needed.

Arguments

• skill-name (required): kebab-case name (e.g., my-skill). Stop if missing or invalid.

Reject --global, explicit destination paths, and other scope overrides. The invocation working directory is the only supported scope.

Resolved Paths

Set <scope> to the working directory where the skill was invoked. Create the source at <scope>/.agents/skills/<name>/ and the Claude Code symlink at <scope>/.claude/skills/<name>. Do not redirect the scope to the repository root when invoked from a nested project or workspace. Never create or modify a skill under ~/.agents, ~/.claude, ~/.codex, or another global installation directory.

The symlink target is always the relative path ../../.agents/skills/<name>.

Skill Layout

<name>/
├── SKILL.md       # Required: frontmatter + lean workflow (aim for <500 lines)
├── agents/
│   └── openai.yaml # Required: Codex metadata; disables implicit invocation
├── scripts/       # Optional: helper code (prefer TypeScript via bun run; Python via uv)
├── references/    # Optional: long-form docs loaded on demand
└── assets/        # Optional: templates / fonts / images used in OUTPUT (never loaded into context)

Agents load skills via progressive disclosure, in three stages:

1. Discovery — only name + description are visible at startup. Front-load triggers in description.
2. Activation — the full SKILL.md body is read once a task matches.
3. Execution — scripts/ run without being read into context; references/ are read only when SKILL.md explicitly links to them.

Keep SKILL.md focused on workflow. Push bulk into scripts/ (deterministic logic) or references/ (documentation).

Authoring Contract

Before choosing a layout, separate the content into:

• Invariants that every valid execution must preserve.
• Preferred defaults that explicit user intent or repository evidence may override.
• Conditional examples and references loaded only when their branch is active.

Define the outcome, authority boundaries, stopping conditions, and completion evidence. Do not prescribe an identical execution path when several safe paths satisfy the same contract. For user-facing workflows, also define which kickoff, progress, decision, blocker, and completion events deserve a message and the smallest useful shape for each.

When to Split Content

Use scripts/ when

• The same code would be rewritten on every invocation (e.g., PDF rotate, JSON transform, curl wrapper).
• Determinism matters more than flexibility (parsing, validation, codegen, idempotent setup).
• A shell pipeline grows past ~5 lines or needs real error handling.
• A long heredoc keeps appearing inside SKILL.md.

Scripts are token-efficient: the agent invokes them without reading them. Document the CLI signature in SKILL.md and leave the implementation in scripts/.

Prefer scripts/*.ts run with bun run scripts/<name>.ts, unless there is a good reason TypeScript is the wrong fit for the helper. Python is also a good choice for data, text, and file processing; run Python helpers through uv run scripts/<name>.py, not raw python or python3.

Use references/ when

• A topic exceeds ~100 lines of prose, examples, or schemas.
• Content is conditionally relevant (variant-, framework-, or domain-specific) — splitting keeps irrelevant context out.
• Detailed API surfaces, DB schemas, policies, or large templates would otherwise dominate SKILL.md.
• A long explanation is needed only on one branch.

Rules of thumb:

• One level deep — link references/placeholder.md directly from SKILL.md, never reference-to-reference.
• Files >100 lines: include a table of contents at the top.
• Files >10k words: document grep patterns in SKILL.md so the agent can locate sections without reading the whole file.
• No duplication — each fact lives in SKILL.md or a reference, never both. Keep skills self-contained rather than sharing references across independently installed skills.
• For every reference, write one line in SKILL.md that says when to read it.

Reference organization patterns

Pattern A — High-level guide + topical references

SKILL.md
references/
├── forms.md
├── api.md
└── examples.md

SKILL.md teaches the happy path; references hold deep-dive material.

Pattern B — Domain or variant split

SKILL.md           # workflow + selection logic
references/
├── aws.md
├── gcp.md
└── azure.md

The agent reads only the variant the user picked — irrelevant providers never enter context.

Pattern C — Conditional details

Inline the basic case in SKILL.md, link advanced files for edge cases (tracked-changes.md, ooxml.md, etc.).

Do NOT add to a skill

• README.md, INSTALLATION.md, CHANGELOG.md, QUICK_REFERENCE.md — extraneous.
• Notes about how the skill was authored, test logs, scratch files.
• Anything the agent will not use at runtime.

Workflow

1. Fetch Agent Skills Docs

Always fetch the latest spec before authoring frontmatter or content:

• https://agentskills.io

Use WebFetch to confirm the current frontmatter schema, naming rules, and progressive-disclosure conventions. Do not guess — the spec evolves.

2. Validate

• Reject names that are not kebab-case or collide with an existing skill at the resolved path.
• Confirm <scope> is the invocation working directory and is not a home-level or global skill directory.
• Stop if <scope>/.agents/skills/<name>/ or <scope>/.claude/skills/<name> already exists.

3. Read the Authoring Guide and Define the Contract and Layout

Read references/writing-great-skills.md before choosing the contract or layout. It defines the predictability levers and the prose-versus-code-or-schema decision.

Then define the observable outcome, invariants, preferred defaults, authority, routing, stop conditions, and completion evidence. While defining routing, identify every skill that the workflow requires, invokes, or hands off to on any supported branch. Exclude suggestions, examples, related-skill references, and underlying tool capabilities. Decide what belongs where:

• Will the workflow invoke helper code? → Prefer scripts/<name>.ts run with bun run; use scripts/<name>.py through uv run when Python is a better fit.
• Machine-consumed schema with a real validator? → Bundle both and document the validation route.
• Reference-only schema documentation, long examples, variant guides, or domain knowledge? → references/<topic>.md
• Templates or files the skill writes into the user's output? → assets/
• None of the above? → ship just SKILL.md.

Sketch the directory tree first, then create only the subdirectories the layout actually needs.

4. Create the Skill

mkdir -p "<scope>/.agents/skills/<name>/agents"
# Add only the subdirectories the layout calls for:
# mkdir -p "<scope>/.agents/skills/<name>/scripts"
# mkdir -p "<scope>/.agents/skills/<name>/references"

Write <scope>/.agents/skills/<name>/SKILL.md with:

• Frontmatter sorted alphabetically, with description last. The description is the only field seen at discovery time — front-load trigger phrases there, not in the body.
• A skill-dependencies array when routing identified dependencies. Use bare names for skills in the same repository and ORG/REPO#SKILL for external skills. Sort by the target skill name (the bare name or substring after #), then by the complete identifier. Omit the field when no dependencies exist.
• A short # Title.
• A one-line summary of what the skill does.
• disable-model-invocation and user-invocable fields set for Claude behavior. Omit only when intentionally relying on Claude defaults: disable-model-invocation: false, user-invocable: true.
• Set coordination: exempt only when the skill's declared default workflow writes no repository files or only repository metadata. This field uses the canonical body sentence This skill is coordination-exempt: skip the ai-coord gate for its declared work. Explicitly authorized escalation beyond the declared behavior re-enters the gate.
• ## Arguments (if any) and a lean imperative workflow. Use fixed steps only when order matters; otherwise state the contract and let repository evidence guide execution.
• Explicit links to every references/ file the workflow may need, each with a one-line note describing when to read it.
• CLI signatures for any bundled scripts, including the runtime command (bun run scripts/<name>.ts or uv run scripts/<name>.py), so the agent can call them without reading them.

Aim for SKILL.md under 500 lines. If a section grows past ~50 lines and is not core workflow, move it to references/ and link it.

Write <scope>/.agents/skills/<name>/agents/openai.yaml with:

policy:
  allow_implicit_invocation: true

Set allow_implicit_invocation to the inverse of SKILL.md disable-model-invocation. If later adding Codex UI metadata or MCP/tool dependencies, merge them into the same file and keep the policy.

5. Create the Claude Code Symlink

Always create a relative symlink so Claude Code picks the skill up from its own discovery path:

mkdir -p "<scope>/.claude/skills"
ln -s "../../.agents/skills/<name>" "<scope>/.claude/skills/<name>"

6. Verify

• Patch tooling creates files at mode 0644. Before the first verification run, chmod 755 every executable under scripts/ and tests/ (a scaffolded test failing its first run with Permission denied (os error 13) is this cause).
• test -f "<scope>/.agents/skills/<name>/SKILL.md"
• test -f "<scope>/.agents/skills/<name>/agents/openai.yaml"
• readlink "<scope>/.claude/skills/<name>" resolves to the source directory.
• test -x every scripts/* and tests/* executable so a missed chmod fails loudly instead of surfacing later as a permission error.
• Finish with ### 🧩 Skill created: <name>, a tree of created paths, and ### ✅ Verified with the exact checks. Link both absolute source and symlink paths.
• Offer to commit the new skill. When the host project's standing instructions require prompt commits, commit without further prompting.

Notes

• Frontmatter rule: sort fields alphabetically, but always place description last.
• skill-dependencies entries must be strings, unique, and must not name the owning skill as a bare dependency. Every bare dependency must resolve to a skill in the same repository; external repository existence is not validated.
• The skills CLI parses SKILL.md frontmatter as YAML before publishing. A colon followed by a space inside a plain scalar, such as leave: freeze in description, makes that parser fail. Use an em dash or another safe separator, or quote the entire scalar.
• "When to use" information belongs in description (discovery-time), not in the body (activation-time only).
• Use imperative / infinitive form throughout SKILL.md.
• All paths inside SKILL.md (e.g., references/placeholder.md, scripts/example.sh) are relative to the skill directory.
• Every new skill must include agents/openai.yaml with policy.allow_implicit_invocation derived from SKILL.md, never the other way around.
• Prefer TypeScript helper scripts run with bun run; use Python through uv run, never raw python or python3.
• Bash scripts inside the skill must be compatible with Bash 3.2 (/bin/bash), since Codex uses the built-in Bash by default.
• Keep helper stdout, commands, paths, frontmatter, and generated skill content undecorated unless that skill's own output contract requires otherwise.