Hook Patterns Skill | Agent Skills

Hook Patterns

Production-tested patterns for Claude Code hooks (1.0.40+).

Hook Roles (Beyond Just Validation)

| Role | Hook Event | Example | |------|------------|---------| | Gate | PreToolUse | Block dangerous commands, require prerequisites | | Side Effect | PostToolUse | Auto-format, auto-commit, lint | | State Manager | PostToolUse | Create/delete state files, track workflow phase | | External Integrator | Any | MCP calls, HTTP APIs, WebSocket | | Context Injector | SessionStart | Load project context, activate services |

Event Reference

| Event | Trigger | Can Block | Use For | |-------|---------|-----------|---------| | SessionStart | Session begins | No | Context loading, service activation | | UserPromptSubmit | User sends message | Yes | Prompt validation, skill suggestion | | PreToolUse | Before tool | Yes | Validation, workflow gates | | PostToolUse | After tool | No | State updates, side effects | | Stop | Claude stops | Yes | Quality gates, cleanup | | SubagentStop | Subagent stops | Yes | Subagent quality gates |

Exit Codes

| Code | PreToolUse/Stop | Others | |------|-----------------|--------| | 0 | Allow | Continue | | 2 | Block (stderr→Claude) | Logged | | 1, 3+ | Block | Logged |

JSON Response (Advanced)

{
  "decision": "approve|block",
  "reason": "Shown to user/Claude",
  "continue": true,
  "suppressOutput": false
}

Quick Registration

{
  "hooks": {
    "PreToolUse": [{
      "matcher": "Edit|Write",
      "hooks": [{ "type": "command", "command": "script.sh", "timeout": 5 }]
    }]
  }
}

Pattern Selection

| Need | Pattern | Reference | |------|---------|-----------| | Force skill/agent activation | Orchestration | orchestration-templates.md | | Block dangerous actions | Gate Pattern | gate-patterns.md | | Auto-format/lint/commit | Side Effect Pattern | side-effect-patterns.md | | Full working examples | Examples | full-examples.md |

Orchestration Patterns (NEW)

Hook-based skill/agent activation with reliability stats:

| Pattern | Success | Use Case | |---------|---------|----------| | Forced Evaluation | 84% | Force Claude to evaluate and use skills | | Agent Router | 100% | Route to plugin agents via Task tool | | Context Injection | 100% | Load project context at session start |

See orchestration-templates.md for templates.

Debugging

Common issues and solutions in debugging-guide.md.

Quick checklist:

Hook executable? (chmod +x)
Using INPUT=$(cat) to read stdin?
Using exit 2 for blocking (not exit 1)?
Debug to stderr (>&2), output to stdout?
New session after settings.json change?

Common Mistakes

Missing nested hooks array
Missing "type": "command"
Using exit 1 instead of exit 2 for blocking
Object matcher (not supported) - use script parsing instead

Agent Skills: Hook Patterns

Install this agent skill to your local

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