Getting it into your agent
This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.
/plugin marketplace add product-on-purpose/agent-skills-toolkit/plugin install agent-skills-toolkitWrote 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/product-on-purpose/agent-skills-toolkit/askit-build-hook)<a href="https://agentmods.dev/skills/product-on-purpose/agent-skills-toolkit/askit-build-hook"><img src="https://agentmods.dev/badge/skills/product-on-purpose/agent-skills-toolkit/askit-build-hook/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/product-on-purpose/agent-skills-toolkit/askit-build-hook"><img src="https://agentmods.dev/badge/skills/product-on-purpose/agent-skills-toolkit/askit-build-hook.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00060 | $0.00762 |
| Opus 5 | $0.00030 | $0.00381 |
| Sonnet 5 | $0.00012 | $0.00152 |
| Haiku 4.5 | $0.00006 | $0.00076 |
Grade A, and why
askit-build-hook 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 10d 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 — 33 lines — stays where its author put it; the contents beside it link to each section on GitHub.
askit-build-hook
Purpose
Author a plugin's hooks: event-driven enforcement or context injection (Standard sec 3.5). Hooks are an Advanced-tier capability. Two modes: create scaffolds a hook and its registration; improve raises an existing hook toward the bar (documentation, idempotency, actionable block messages). The hook SKILL is portable; what it authors is primarily a Claude capability (31 events) with a smaller Codex event set. Authoring depth is in references/authoring-hooks.md. Follows the shared builder contract (../../docs/reference/builder-pattern.md).
When to use
When the user asks to add, scaffold, author, or improve a hook (a PreToolUse / PostToolUse / Stop / SessionStart guard, a context injector, or any event-driven automation) for a plugin.
create mode
- Brief interview: the event (for example PreToolUse), the trigger or matcher, the hook type (
command/http/mcp_tool/prompt/agent), the scope (what it guards or injects), and the failure behavior (fail-safe block vs warn). Skip the interview if these are in context. - Author the hook and its registration. A plugin registers hooks in
hooks/hooks.jsonusing${CLAUDE_PLUGIN_ROOT}; copytemplates/hooks.jsonif none exists. Document the event, trigger, scope, and failure behavior (Standard sec 3.5 MUST). - For a blocking hook (for example a PreToolUse deny), write an ACTIONABLE message that states what was blocked and how to proceed. Make the hook idempotent where the event can repeat.
- Register the hook in
library.jsoncomponents.hooksas{ name, version, tier, status }. - Targets: Claude supports 31 events. Codex supports a smaller set (PreToolUse, PostToolUse, Pre/PostCompact, SessionStart, SubagentStart/Stop, UserPromptSubmit, Stop, PermissionRequest). Verify current Codex plugin-hook ingestion at build time (a known caveat) and scope
agent-targetsaccordingly. - Assess with
node scripts/evaluate.mjs . --json. Hook documentation and idempotency are graded at the Advanced tier; the deterministic hook check lands with Gold self-hosting (Phase 5).
What ships with it
10 files 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.
- examples/anti-wrong-exit-code.md 5.3 KB
- examples/anti-wrong-exit-code.mjs 1.4 KB runs code
- examples/golden-1-generated-file-guard.md 4.7 KB
- examples/golden-1-generated-file-guard.mjs 3.0 KB runs code
- examples/golden-2-trailing-whitespace-formatter.md 5.7 KB
- examples/golden-2-trailing-whitespace-formatter.mjs 2.5 KB runs code
- examples/golden-3-stop-uncommitted-notifier.md 4.7 KB
- examples/golden-3-stop-uncommitted-notifier.mjs 1.9 KB runs code
- README.md 633 B
- references/authoring-hooks.md 13 KB
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.
- 10d ago First seen · 33 lines · 60 tokens per session scan A ac9223d1a264
askit-build-hook is a skill published in the GitHub repository product-on-purpose/agent-skills-toolkit (2 stars, last pushed today), licensed Apache-2.0. It adds 60 tokens to every session and 762 once invoked, about $0.0003 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 2026-08-31.
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