Hook Development Rules

When working with files in .claude/hooks/:

Pattern

Shell wrapper (.sh) → TypeScript (.ts) via npx tsx

Shell Wrapper Template

#!/bin/bash
set -e
cd "$CLAUDE_PROJECT_DIR/.claude/hooks"
cat | npx tsx <handler>.ts

TypeScript Handler Pattern

interface HookInput {
  // Event-specific fields
}

async function main() {
  const input: HookInput = JSON.parse(await readStdin());

  // Process input

  const output = {
    result: 'continue',  // or 'block'
    message: 'Optional system reminder'
  };

  console.log(JSON.stringify(output));
}

Hook Events

• PreToolUse - Before tool execution (can block)
• PostToolUse - After tool execution
• UserPromptSubmit - Before processing user prompt
• PreCompact - Before context compaction
• SessionStart - On session start/resume/compact
• Stop - When agent finishes

Testing

Test hooks manually:

echo '{"type": "resume"}' | .claude/hooks/session-start-continuity.sh

Registration

Add hooks to .claude/settings.json:

{
  "hooks": {
    "EventName": [{
      "matcher": ["pattern"],  // Optional
      "hooks": [{
        "type": "command",
        "command": "$CLAUDE_PROJECT_DIR/.claude/hooks/hook.sh"
      }]
    }]
  }
}