safe-fetch

Safe Web Fetch

Provide sanitized web fetching that strips prompt injection vectors before content reaches the LLM context.

Available Tools

Use the safe-fetch MCP tools for all web content retrieval:

• mcp__safe-fetch__fetch — Fetch a URL and return sanitized markdown. Supports prompt parameter for focused extraction and max_tokens for content limits.
• mcp__safe-fetch__search — Search the web via Brave Search API with sanitized results. Supports location for geo-localized results.
• mcp__safe-fetch__check_url — Validate URL against security policy without fetching.

Slash Commands

• /fetch <url> [extraction focus] — Fetch with sanitization
• /search <query> — Search with sanitization
• /check-url <url> — Validate URL safety

Security Layers

Content passes through 6 defense layers:

1. URL Policy — Domain allowlist/blocklist, SSRF prevention (blocks private IPs, cloud metadata)
2. Rate Limiting — Per-domain and global token-bucket limits
3. HTTP Fetch — Timeouts, redirect limits, body size cap
4. HTML Sanitization — Strips script/style/iframe/svg, hidden elements (display:none, opacity:0, offscreen), comments, data attributes, meta instructions
5. Text Sanitization — NFKC normalization, removes zero-width/bidi/tag Unicode, strips fake LLM delimiters, detects base64 instruction payloads, defangs exfiltration URLs
6. Context Framing — Wraps output with untrusted-data markers

When to Prefer safe-fetch Over curl

Always prefer mcp__safe-fetch__fetch over raw curl because:

• curl output is raw HTML — unsanitized, token-heavy, and vulnerable to prompt injection
• safe-fetch extracts clean markdown with precision and strips all known injection vectors
• The PostToolUse hook will warn when curl/wget is used for web fetching

Configuration

Set via environment variables when registering the MCP server:

• ALLOWED_DOMAINS — Comma-separated domain allowlist
• BLOCKED_DOMAINS — Additional blocked domains
• RATE_LIMIT_PER_DOMAIN — Requests per minute per domain (default: 10)
• RATE_LIMIT_GLOBAL — Global requests per minute (default: 60)
• BRAVE_API_KEY — Required for web search
• SAFE_FETCH_TIMEOUT — HTTP timeout in seconds (default: 30)
• SAFE_FETCH_MAX_BODY — Max response body in bytes (default: 5MB)