jstockdi · January 30, 2026 16:05
diff --git a/gistfile0.txt b/gistfile0.txt
 # Implementing PII Validation Hooks in Claude Code

 Hooks are shell commands that run at specific points in Claude Code's workflow. For PII protection, you'll use PreToolUse hooks to inspect and block operations before they execute.

 ## Step 1: Create the PII Validation Script

 Create a file at `.claude/hooks/pii_validator.py`:

 ```python
 #!/usr/bin/env python3
 """
 PII Validator Hook for Claude Code
 Blocks file writes and commands that contain potential PII.
 """

 import json
 import sys
 import re

 # PII patterns to detect
 PII_PATTERNS = {
    'ssn': r'\b\d{3}-\d{2}-\d{4}\b',
    'credit_card': r'\b\d{4}[- ]?\d{4}[- ]?\d{4}[- ]?\d{4}\b',
    'email': r'\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b',
    'phone': r'\b(\+1[- ]?)?\(?\d{3}\)?[- ]?\d{3}[- ]?\d{4}\b',
    'api_key': r'\b(sk-[a-zA-Z0-9]{20,}|api[_-]?key[=:]\s*["\']?[a-zA-Z0-9]{20,})\b',
    'aws_key': r'\b(AKIA[0-9A-Z]{16})\b',
    'password': r'(password|passwd|pwd)\s*[=:]\s*["\']?[^\s"\']+',
 }

 def detect_pii(text: str) -> list[tuple[str, str]]:
    """Scan text for PII patterns. Returns list of (pii_type, matched_value)."""
    findings = []
    for pii_type, pattern in PII_PATTERNS.items():
        matches = re.findall(pattern, text, re.IGNORECASE)
        for match in matches:
            # Redact the actual value for safety
            redacted = match[:4] + '***' if len(match) > 4 else '***'
            findings.append((pii_type, redacted))
    return findings

 def main():
    # Read hook input from stdin
    input_data = json.load(sys.stdin)
    
    tool_name = input_data.get('tool_name', '')
    tool_input = input_data.get('tool_input', {})
    
    content_to_check = ""
    context = ""
    
    # Extract content based on tool type
    if tool_name in ('Write', 'Edit', 'MultiEdit'):
        content_to_check = tool_input.get('content', '')
        context = f"file: {tool_input.get('file_path', 'unknown')}"
    
    elif tool_name == 'Bash':
        content_to_check = tool_input.get('command', '')
        context = "bash command"
    
    elif tool_name == 'WebFetch':
        # Check if URL contains sensitive data
        content_to_check = tool_input.get('url', '')
        context = "web request URL"
    
    # Scan for PII
    findings = detect_pii(content_to_check)
    
    if findings:
        # Block the operation and provide feedback
        pii_types = ', '.join(set(f[0] for f in findings))
        
        output = {
            "hookSpecificOutput": {
                "hookEventName": "PreToolUse",
                "permissionDecision": "deny",
                "userFacingText": f"🛑 PII BLOCKED: Detected {pii_types} in {context}",
                "assistantFacingText": (
                    f"SECURITY BLOCK: Your {tool_name} operation was blocked because it "
                    f"contains potential PII ({pii_types}). Please remove or redact "
                    f"sensitive information before proceeding. Detected patterns: "
                    f"{[f[1] for f in findings]}"
                )
            }
        }
        print(json.dumps(output))
        sys.exit(2)  # Exit code 2 = block with feedback
    
    # Allow the operation
    sys.exit(0)

 if __name__ == "__main__":
    main()
 ```

 ## Step 2: Make it Executable

 ```bash
 chmod +x .claude/hooks/pii_validator.py
 ```

 ## Step 3: Configure the Hook in Settings

 Add to your `.claude/settings.json`:

 ```json
 {
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Write|Edit|MultiEdit|Bash|WebFetch",
        "hooks": [
          {
            "type": "command",
            "command": "python3 \"$CLAUDE_PROJECT_DIR/.claude/hooks/pii_validator.py\"",
            "timeout": 10
          }
        ]
      }
    ]
  }
 }
 ```

 ## Step 4: Register the Hook

 In Claude Code, run:
 ```
 /hooks
 ```

 Then review and approve the new hook configuration.

 ## How It Works

 | Exit Code | Behavior |
 |-----------|----------|
 | 0 | Allow the operation to proceed |
 | 2 | Block and provide feedback to Claude |
 | Non-zero (other) | Block silently |

 The hook receives JSON on stdin with the tool details:

 ```json
 {
  "tool_name": "Write",
  "tool_input": {
    "file_path": "/path/to/file.txt",
    "content": "file content here..."
  }
 }
 ```

 ## Extended Example: Adding Custom Patterns

 For your KYC/fintech context, you might want to add patterns like:

 ```python
 PII_PATTERNS = {
    # ... existing patterns ...
    'sin': r'\b\d{3}[- ]?\d{3}[- ]?\d{3}\b',  # Canadian SIN
    'passport': r'\b[A-Z]{2}\d{6}\b',
    'account_number': r'\baccount[_\s]?(num|number|#)?[:\s]*\d{8,12}\b',
    'routing_number': r'\brouting[_\s]?(num|number|#)?[:\s]*\d{9}\b',
 }
 ```

 ---

 Would you like me to expand this with additional validation logic, like checking for PII in file paths or adding logging/alerting capabilities?
	# Implementing PII Validation Hooks in Claude Code

	Hooks are shell commands that run at specific points in Claude Code's workflow. For PII protection, you'll use PreToolUse hooks to inspect and block operations before they execute.

	## Step 1: Create the PII Validation Script

	Create a file at `.claude/hooks/pii_validator.py`:

	```python
	#!/usr/bin/env python3
	"""
	PII Validator Hook for Claude Code
	Blocks file writes and commands that contain potential PII.
	"""

	import json
	import sys
	import re

	# PII patterns to detect
	PII_PATTERNS = {
	'ssn': r'\b\d{3}-\d{2}-\d{4}\b',
	'credit_card': r'\b\d{4}[- ]?\d{4}[- ]?\d{4}[- ]?\d{4}\b',
	'email': r'\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z\|a-z]{2,}\b',
	'phone': r'\b(\+1[- ]?)?\(?\d{3}\)?[- ]?\d{3}[- ]?\d{4}\b',
	'api_key': r'\b(sk-[a-zA-Z0-9]{20,}\|api[_-]?key[=:]\s*["\']?[a-zA-Z0-9]{20,})\b',
	'aws_key': r'\b(AKIA[0-9A-Z]{16})\b',
	'password': r'(password\|passwd\|pwd)\s[=:]\s["\']?[^\s"\']+',
	}

	def detect_pii(text: str) -> list[tuple[str, str]]:
	"""Scan text for PII patterns. Returns list of (pii_type, matched_value)."""
	findings = []
	for pii_type, pattern in PII_PATTERNS.items():
	matches = re.findall(pattern, text, re.IGNORECASE)
	for match in matches:
	# Redact the actual value for safety
	redacted = match[:4] + '*' if len(match) > 4 else '*'
	findings.append((pii_type, redacted))
	return findings

	def main():
	# Read hook input from stdin
	input_data = json.load(sys.stdin)

	tool_name = input_data.get('tool_name', '')
	tool_input = input_data.get('tool_input', {})

	content_to_check = ""
	context = ""

	# Extract content based on tool type
	if tool_name in ('Write', 'Edit', 'MultiEdit'):
	content_to_check = tool_input.get('content', '')
	context = f"file: {tool_input.get('file_path', 'unknown')}"

	elif tool_name == 'Bash':
	content_to_check = tool_input.get('command', '')
	context = "bash command"

	elif tool_name == 'WebFetch':
	# Check if URL contains sensitive data
	content_to_check = tool_input.get('url', '')
	context = "web request URL"

	# Scan for PII
	findings = detect_pii(content_to_check)

	if findings:
	# Block the operation and provide feedback
	pii_types = ', '.join(set(f[0] for f in findings))

	output = {
	"hookSpecificOutput": {
	"hookEventName": "PreToolUse",
	"permissionDecision": "deny",
	"userFacingText": f"🛑 PII BLOCKED: Detected {pii_types} in {context}",
	"assistantFacingText": (
	f"SECURITY BLOCK: Your {tool_name} operation was blocked because it "
	f"contains potential PII ({pii_types}). Please remove or redact "
	f"sensitive information before proceeding. Detected patterns: "
	f"{[f[1] for f in findings]}"
	)
	}
	}
	print(json.dumps(output))
	sys.exit(2) # Exit code 2 = block with feedback

	# Allow the operation
	sys.exit(0)

	if __name__ == "__main__":
	main()
	```

	## Step 2: Make it Executable

	```bash
	chmod +x .claude/hooks/pii_validator.py
	```

	## Step 3: Configure the Hook in Settings

	Add to your `.claude/settings.json`:

	```json
	{
	"hooks": {
	"PreToolUse": [
	{
	"matcher": "Write\|Edit\|MultiEdit\|Bash\|WebFetch",
	"hooks": [
	{
	"type": "command",
	"command": "python3 \"$CLAUDE_PROJECT_DIR/.claude/hooks/pii_validator.py\"",
	"timeout": 10
	}
	]
	}
	]
	}
	}
	```

	## Step 4: Register the Hook

	In Claude Code, run:
	```
	/hooks
	```

	Then review and approve the new hook configuration.

	## How It Works

	\| Exit Code \| Behavior \|
	\|-----------\|----------\|
	\| 0 \| Allow the operation to proceed \|
	\| 2 \| Block and provide feedback to Claude \|
	\| Non-zero (other) \| Block silently \|

	The hook receives JSON on stdin with the tool details:

	```json
	{
	"tool_name": "Write",
	"tool_input": {
	"file_path": "/path/to/file.txt",
	"content": "file content here..."
	}
	}
	```

	## Extended Example: Adding Custom Patterns

	For your KYC/fintech context, you might want to add patterns like:

	```python
	PII_PATTERNS = {
	# ... existing patterns ...
	'sin': r'\b\d{3}[- ]?\d{3}[- ]?\d{3}\b', # Canadian SIN
	'passport': r'\b[A-Z]{2}\d{6}\b',
	'account_number': r'\baccount[_\s]?(num\|number\|#)?[:\s]*\d{8,12}\b',
	'routing_number': r'\brouting[_\s]?(num\|number\|#)?[:\s]*\d{9}\b',
	}
	```

	---

	Would you like me to expand this with additional validation logic, like checking for PII in file paths or adding logging/alerting capabilities?
No results found