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.
npx skills add terrene-foundation/kailash-coc-claude-py --skill hook-authoringgit clone --depth 1 https://github.com/terrene-foundation/kailash-coc-claude-pyWrote 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/terrene-foundation/kailash-coc-claude-py/hook-authoring)<a href="https://agentmods.dev/skills/terrene-foundation/kailash-coc-claude-py/hook-authoring"><img src="https://agentmods.dev/badge/skills/terrene-foundation/kailash-coc-claude-py/hook-authoring/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/terrene-foundation/kailash-coc-claude-py/hook-authoring"><img src="https://agentmods.dev/badge/skills/terrene-foundation/kailash-coc-claude-py/hook-authoring.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Prompt Injection · line 26 Large whitespace padding was detected (a block of blank lines or a long run of spaces). This can push injected instructions below or to the right of the visible area so a human reviewer never sees them while the agent still reads them. Manual review of the hidden content is recommended.Fix: Remove the large whitespace padding (blank-line blocks or long space runs) and review any content hidden below or to the right of it. Keep skill files compact and reviewable so no instructions can be
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 | $0.00046 | $0.05026 |
| Opus 5 | $0.00023 | $0.02513 |
| Sonnet 5 | $0.00009 | $0.01005 |
| Haiku 4.5 | $0.00005 | $0.00503 |
Grade A, and why
hook-authoring 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 — 274 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Hook Authoring
Reference for authoring and auditing event hooks across CC, Codex, and Gemini. Hooks are L3 (Guardrails) artifacts in the COC 5-layer architecture per rules/cc-artifacts.md — alongside rules, but distinguished by deterministic runtime invocation on tool / session lifecycle events. Sibling to skill-authoring (F1) and command-authoring (F2).
When To Use
Authoring a new hook script under .claude/hooks/. Auditing an existing hook for timeout discipline, output shape, severity grounding, predicate bijection with the MCP guard, or path resolution across CLIs. Deciding whether enforcement belongs in a hook (runtime tripwire, deterministic), an agent (judgment, tools), or a rule (always-on prose guardrail).
Quick Reference
| CLI | Registration | Event surface | Path env |
|---|---|---|---|
| CC | .claude/settings.json hooks block |
SessionStart, UserPromptSubmit, PreToolUse, PostToolUse, Stop |
$CLAUDE_PROJECT_DIR exported |
| Codex | .codex/hooks.json (repo) or ~/.codex/hooks.json (user) |
Same names; Bash tool only — apply_patch / Write / MCP do NOT fire |
NOT exported; resolve via cwd-relative |
| Gemini | .gemini/settings.json hooks object |
BeforeTool / AfterTool / BeforeAgent / SessionStart / SessionEnd |
$GEMINI_PROJECT_DIR exported |
| Constraint | Value |
|---|---|
| Script location | .claude/hooks/<name>.js — Anthropic-documented path, shared across all three CLIs |
| Module system | CommonJS (require), matching repo convention |
| Timeout fallback | Mandatory per rules/cc-artifacts.md Rule 7 — setTimeout → emit {continue: true}, process.exit(1) |
| Stdin / stdout | Read JSON payload from stdin; emit JSON on stdout |
| Halting exit (PreToolUse) | process.exit(2) — but ONLY via lib/instruct-and-wait.js::emit() shape per rules/hook-output-discipline.md |
| Halting return (post) | continue: false — ONLY via the same emit() shape |
| Block severity | Requires structural / behavioral / AST signal — lexical regex match is BLOCKED per hook-output-discipline.md MUST-2 |
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 · 274 lines · 46 tokens per session scan A a8729d0e60f7
hook-authoring is a skill published in the GitHub repository terrene-foundation/kailash-coc-claude-py (12 stars, last pushed 24d ago), licensed Apache-2.0. It adds 46 tokens to every session and 5,026 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 2026-09-03.
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