Project Hooks

Project Hooks

Create project-specific hooks that only run in a specific workspace.

Quick Setup

# 1. Create hooks directory
mkdir -p .claude/hooks

# 2. Create settings.json with hook config (see templates below)

Hook Locations

settings.json Structure

Create .claude/settings.json in your project root:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash|Edit|Write",
        "command": ".claude/hooks/pre-tool.sh"
      }
    ],
    "PostToolUse": [
      {
        "matcher": "*",
        "command": ".claude/hooks/post-tool.sh"
      }
    ],
    "UserPromptSubmit": [
      {
        "command": ".claude/hooks/on-prompt.sh"
      }
    ]
  }
}

Hook Events

Matcher Patterns

• "*" - Match all tools
• "Bash" - Match specific tool
• "Bash|Edit|Write" - Match multiple tools (OR)
• "mcp__playwright__*" - Wildcard patterns

Hook Input/Output

Input (stdin)

{
  "event": "PreToolUse",
  "tool": "Bash",
  "input": {"command": "ls -la"},
  "session_id": "abc123"
}

Output (stdout)

{
  "decision": "allow",
  "message": "Optional message to show"
}

Decisions

• "allow" - Proceed normally
• "block" - Stop the action
• "modify" - Change the input (with modifiedInput)

Templates

Template 1: Lint on Save (TypeScript)

.claude/settings.json:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "command": ".claude/hooks/lint-on-save.sh"
      }
    ]
  }
}

.claude/hooks/lint-on-save.sh:

#!/bin/bash
INPUT=$(cat)
FILE=$(echo "$INPUT" | jq -r '.input.file_path // empty')

if [[ "$FILE" == *.ts || "$FILE" == *.tsx ]]; then
  npx eslint --fix "$FILE" 2>/dev/null
fi

echo '{"continue": true}'

Template 2: Block Dangerous Commands

.claude/hooks/block-dangerous.sh:

#!/bin/bash
INPUT=$(cat)
CMD=$(echo "$INPUT" | jq -r '.input.command // empty')

# Block rm -rf /
if echo "$CMD" | grep -qE 'rm\s+-rf\s+/[^/]'; then
  echo '{"decision": "block", "message": "Blocked dangerous rm command"}'
  exit 0
fi

echo '{"decision": "allow"}'

Template 3: Auto-Format Python

.claude/hooks/format-python.sh:

#!/bin/bash
INPUT=$(cat)
FILE=$(echo "$INPUT" | jq -r '.input.file_path // empty')

if [[ "$FILE" == *.py ]]; then
  black "$FILE" 2>/dev/null
  ruff check --fix "$FILE" 2>/dev/null
fi

echo '{"continue": true}'

Template 4: Project Context Injection

.claude/hooks/inject-context.sh:

#!/bin/bash
# Inject project-specific context into every prompt
echo '{"message": "Project: MyApp | Stack: React + Supabase"}'

Template 5: Run Tests After Changes

.claude/hooks/run-tests.sh:

#!/bin/bash
INPUT=$(cat)
FILE=$(echo "$INPUT" | jq -r '.input.file_path // empty')

# Run tests for changed file
if [[ "$FILE" == *.ts && "$FILE" != *.test.ts ]]; then
  TEST_FILE="${FILE%.ts}.test.ts"
  if [[ -f "$TEST_FILE" ]]; then
    npm test -- "$TEST_FILE" 2>/dev/null &
  fi
fi

echo '{"continue": true}'

Scaffold Command

Run this to scaffold hooks for any project:

mkdir -p .claude/hooks && echo '{"hooks":{}}' > .claude/settings.json

Debugging Hooks

Test hook manually

echo '{"event":"PreToolUse","tool":"Bash","input":{"command":"ls"}}' | .claude/hooks/my-hook.sh

Add logging

echo "[$(date)] $INPUT" >> /tmp/hook-debug.log

Best Practices

1. Keep hooks fast - Slow hooks delay every action
2. Always output valid JSON - Invalid JSON = hook failure
3. Use #!/bin/bash - Explicit shebang
4. Make executable - chmod +x .claude/hooks/*.sh
5. Handle missing tools - Check if eslint/black exist before running