Claude Code PreToolUse hook for WebFetch matcher

claude-pre_tool_use-hook_webfetch.py

#!/usr/bin/env python3
import json
import re
import sys

# Define validation rules as a list of (regex pattern, message) tuples
VALIDATION_RULES = [
    (
        r"https://www.notion.so/",
        "Notion ページへのアクセスには WebFetch ツールではなく mcp__notion を利用してください",
    ),
    (
        r"https://github.com/",
        "GitHub へのアクセスには WebFetch ツールではなく gh コマンドを利用してください",
    ),
]

def validate_url(url: str) -> list[str]:
    issues = []
    for pattern, message in VALIDATION_RULES:
        if re.search(pattern, url):
            issues.append(message)
    return issues


try:
    input_data = json.load(sys.stdin)
except json.JSONDecodeError as e:
    print(f"Error: Invalid JSON input: {e}", file=sys.stderr)
    sys.exit(1)

tool_name = input_data.get("tool_name", "")
tool_input = input_data.get("tool_input", {})
url = tool_input.get("url", "")

if tool_name != "WebFetch":
    sys.exit(1)

# Validate the url
issues = validate_url(url)

if issues:
    for message in issues:
        print(f"• {message}", file=sys.stderr)
    sys.exit(2)