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 agentmods add agents/ibrain-bvba/gutt-claude-code-plugin/hook-expertgit clone --depth 1 https://github.com/iBrain-BVBA/gutt-claude-code-pluginWhat 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 | $0.00036 | $0.03121 |
| Opus 5 | $0.00018 | $0.01561 |
| Sonnet 5 | $0.00007 | $0.00624 |
| Haiku 4.5 | $0.00004 | $0.00312 |
Grade A, and why
hook-expert scanned grade A with 1 finding 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.
Runs shell commandslowCapability
Expected in a hook, worth knowing in a rule or an instructions file.
node -e "const fs=require('fs'),p=require('path'),t=p.join(require('os').tmpdir(),'h.json');fs.writeFileSync(t,JSON.stringify({session_id:'debug-001',tool_name:'Task',tool_input:{prompt:'test'}}));console.log(require('ch How it starts
The opening of the file, as written. The whole thing — 291 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Hook Expert Agent
Deep specialist in the gutt-pro hook system. Focuses on debugging hook failures, diagnosing state corruption, optimizing hook performance, resolving cross-platform issues, and understanding the full interaction between hooks, shared libraries, and IDE lifecycle events.
Trigger
Invoke this agent when:
- A hook is silently failing or producing unexpected output
- State files under
${CLAUDE_PLUGIN_DATA}appear corrupt or stale - Hooks work in Claude Code but fail in Cursor (or vice versa)
- Hook execution is slow or causing IDE lag
- Debugging complex interactions between multiple hooks
- Investigating race conditions in parallel subagent hooks
- User asks "why isn't this hook working?" or "debug hook X"
Do NOT invoke for: Basic hook creation or registration — use plugin-dev instead.
Hook Architecture
CommonJS Requirement
All hooks MUST be CommonJS (.cjs). The project uses ES modules ("type": "module" in package.json), but hooks require .cjs for synchronous IDE execution. Every hook must:
- Consume all stdin (even if unused) to avoid broken pipe errors
- Parse stdin as JSON
- Process the event
- Exit with code 0 (unless intentionally blocking)
Lifecycle Events
| Event | When Fired | Stdin Fields | Expected Output |
|---|---|---|---|
SessionStart |
New session begins | session_id, cwd |
Setup messages or empty |
UserPromptSubmit |
User submits prompt | session_id, user_prompt |
Modified prompt or empty |
PreToolUse |
Before tool executes | session_id, tool_name, tool_input |
JSON with decision or additionalContext |
PostToolUse |
After tool executes | session_id, tool_name, tool_input, tool_result |
followup_message or empty |
SubagentStart |
Subagent spawned | session_id, agent_type, agent_prompt |
Context injection or empty |
SubagentStop |
Subagent completes | session_id, agent_type, agent_result |
Capture or empty |
Stop |
Task completes | session_id, stop_hook_output |
Summary or empty |
statusLine |
HUD refresh | session_id |
Single-line string |
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 · 291 lines · 36 tokens per session scan A 9482af4e4e84
hook-expert is an agent published in the GitHub repository iBrain-BVBA/gutt-claude-code-plugin (4 stars, last pushed 12d ago), licensed MIT. It adds 36 tokens to every session and 3,121 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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