A workflow for creating a custom Claude Code or Codex skill. A skill is a reusable instruction file that tells a coding agent when and how to handle a particular kind of task.

Use it to draft or scaffold a skill in the appropriate project directory, including its instructions and optional Codex configuration.

It collects missing details before writing the skill and avoids inventing its name, tools, or behavior. It also follows the required file formats for each agent.

ad-skill — Skill by CorridorTech

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 skills/corridortech/posecap/ad-skill

Any agent

npx skills add CorridorTech/PoseCap --skill ad-skill

Clone the repo

git clone --depth 1 https://github.com/CorridorTech/PoseCap

Made for: Claude Code, Codex.

Per session 88 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 853 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	$0.00088	$0.00853
Opus 5	$0.00044	$0.00426
Sonnet 5	$0.00018	$0.00171
Haiku 4.5	$0.00009	$0.00085

Measured 2d ago against content hash 80fb44cc91d5, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

ad-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.

.agents/skills/ad-skill/SKILL.md · 50 lines

What it actually says

<background_information> Drafts .claude/skills/<name>/SKILL.md (Claude Code) or .agents/skills/<name>/SKILL.md plus agents/openai.yaml (Codex). Spec: code.claude.com/docs/en/skills. Open standard: agentskills.io. Examples: github.com/anthropics/skills. </background_information>

Step 2 — interview to fill. Ask one question per missing field, in this order:

What it does — one sentence, primary triggering signal.
When to invoke — common task framings the user would say. Combined description + when_to_use is capped at 1,536 chars per the Anthropic spec.
Tools needed — Read, Write, Glob, Grep, Bash, Task, ... Restrict to what the skill actually uses.
Body shape — instructions, optional template, output contract. Keep ≤500 lines; move long material to sibling files (reference.md, examples.md, scripts/).

Do NOT invent values. When the user does not know something, ask. Do NOT invent fields not in the spec — only declare frontmatter fields that actually apply.

Step 3 — write the file(s).

Path:

Claude Code project: .claude/skills/<name>/SKILL.md
Claude Code personal: ~/.claude/skills/<name>/SKILL.md
Codex project: .agents/skills/<name>/SKILL.md plus .agents/skills/<name>/agents/openai.yaml (cc-sdd convention).

Frontmatter per agent:

Claude Code: name, description, allowed-tools (and any other field from the spec the user asked for).
Codex: minimal frontmatter — name, description. Body uses XML tags (<background_information>, <instructions>, <template>, <output_contract>). The agents/openai.yaml carries interface.display_name, interface.short_description, policy.allow_implicit_invocation.

Body: imperative instructions ("do X", not "this skill does X"). Every line is recurring token cost once the skill loads — be terse. Don't restate AGENTS.md.

Step 4 — stop after writing. Do not invoke the new skill, do not pre-fill it with example content, do not test it. The user will exercise it themselves.

<output_contract> A single new SKILL.md at the chosen path (plus agents/openai.yaml for Codex). Frontmatter declares only the fields actually used. Body is imperative and terse. No external file dependencies the user did not ask for. </output_contract>

Test the new skill's description triggers by invoking it from a real conversation — verify auto-triggering on the keywords you chose.
If the skill is meant to be universal across the kit's profiles, propose an ADR + Task to add it to the profile catalog (src/lib/profiles.js).
If the skill carries a sibling subagent, declare it in manifest.json and add the source under agents/.

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.

agents/openai.yaml 178 B

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 · 50 lines · 88 tokens per session scan A 80fb44cc91d5

Subscribe to this mod's changes

ad-skill is a skill published in the GitHub repository CorridorTech/PoseCap (190 stars, last pushed 10d ago), licensed Apache-2.0. It adds 88 tokens to every session and 853 once invoked, about $0.0004 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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ad-skill