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 skills/dwmkerr/claude-toolkit/claude-code-hook-developmentnpx skills add dwmkerr/claude-toolkit --skill claude-code-hook-developmentgit clone --depth 1 https://github.com/dwmkerr/claude-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/dwmkerr/claude-toolkit/claude-code-hook-development)<a href="https://agentmods.dev/skills/dwmkerr/claude-toolkit/claude-code-hook-development"><img src="https://agentmods.dev/badge/skills/dwmkerr/claude-toolkit/claude-code-hook-development.svg" alt="Measured on agentmods" 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 | $0.00069 | $0.01240 |
| Opus 5 | $0.00034 | $0.00620 |
| Sonnet 5 | $0.00014 | $0.00248 |
| Haiku 4.5 | $0.00007 | $0.00124 |
Grade B, and why
claude-code-hook-development scanned grade B 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 3d 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.
Reads agent configuration directoriesmediumAgent snooping
.claude/, .codex/, .gemini/ hold keys, settings and other credentials a mod has no legitimate need for.
3. **Validate JSON** - Run `cat .claude/settings.json | jq .` to check syntax How it starts
The opening of the file, as written. The whole thing — 161 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Claude Code Hook Development
Create hooks that run shell commands on specific events to add guardrails, automations, and policy enforcement.
Quick Reference
You MUST read the reference files for detailed schemas and examples:
- Hook Events Reference - All events with input/output schemas
- Examples: Firewall - Block dangerous commands
- Examples: Quality Checks - Lint/format after edits
- Examples: Pre-Push Tests - Run tests before git push
Core Concepts
Hook Types
- Command hooks - Run bash scripts
- Prompt hooks - Query LLM for context-aware decisions
Exit Codes
| Code | Meaning | Behavior |
|---|---|---|
| 0 | Success | Action proceeds; stdout shown in verbose mode |
| 2 | Block | Action blocked; stderr fed to Claude |
| Other | Error | Non-blocking; stderr shown to user |
File Locations
- Settings:
.claude/settings.json - Scripts:
.claude/hooks/(mark executable)
Settings Structure
{
"hooks": {
"PreToolUse": [
{
"matcher": "Bash",
"hooks": [
{
"type": "command",
"command": ".claude/hooks/my-script.sh",
"timeout": 60
}
]
}
]
}
}
Hook Events Summary
| Event | When | Can Block? |
|---|---|---|
| PreToolUse | Before tool executes | Yes (exit 2) |
| PostToolUse | After tool completes | Feedback only |
| PermissionRequest | User sees permission dialog | Yes |
| UserPromptSubmit | User submits prompt | Yes |
| Stop | Main agent finishes | Yes (continue) |
| SubagentStop | Subagent finishes | Yes (continue) |
| SessionStart | Session begins | Add context |
| SessionEnd | Session ends | Cleanup only |
| Notification | Notifications sent | No |
| PreCompact | Before compact | No |
Common Matchers
For PreToolUse/PostToolUse/PermissionRequest:
Bash- Shell commandsEdit,Write,Read- File operationsGlob,Grep- Search operationsTask- Subagent tasksmcp__<server>__<tool>- MCP tools- Regex patterns supported
What ships with it
5 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.
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.
- 3d ago First seen · 161 lines · 69 tokens per session scan B 3256d5568cf2
claude-code-hook-development is a skill published in the GitHub repository dwmkerr/claude-toolkit (23 stars, last pushed 9d ago), licensed MIT. It adds 69 tokens to every session and 1,240 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it B with 1 finding (reads agent configuration directories). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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