🛡️ fast-mcp-gatekeeper

The Zero-Latency Security & Policy Proxy for Model Context Protocol (MCP)
Powered by TypeSafe AI's Jev System 1 Decision Model.

As coding assistants (Cursor, Claude Desktop, Antigravity) gain access to local tools via the Model Context Protocol (MCP), granting unconstrained access to your filesystem, terminal, and database is risky.

Existing security checks run through heavy LLMs add 2,000–3,000ms of latency to every single tool call, crippling agent responsiveness.

fast-mcp-gatekeeper acts as an ultra-fast stdio proxy sitting between your MCP client and any MCP server. It inspects all JSON-RPC tools/call packets in <50 milliseconds, detecting path traversals, command injections, and credential leaks without slowing down your AI workflow.

✨ Features

• ⚡ Sub-50ms Overhead: Jev evaluates tool arguments in a single non-autoregressive pass.

• 🛑 Automatic Interception: Returns standard MCP JSON-RPC -32001 error codes before the downstream tool can ever execute.

• 🔑 Automatic Token Sanitization: Redacts leaked API keys (sk-..., Bearer tokens, passwords) on the fly with the redact policy.

• 🔌 Universal Compatibility: Works with any stdio-based MCP server (e.g. @modelcontextprotocol/server-filesystem, Postgres, Git, GitHub).

Related MCP server: MCP Security Gateway

🚀 Quick Setup with Claude Desktop or Cursor

In your claude_desktop_config.json or Cursor MCP settings, simply prepend fast-mcp-gatekeeper -- to your server command:

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": [
        "-y",
        "fast-mcp-gatekeeper",
        "--",
        "npx",
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/Users/username/workspace"
      ]
    }
  }
}

🧪 CLI Inspection Demo

You can inspect any simulated tool call directly from the terminal:

npx fast-mcp-gatekeeper --inspect '{"name": "read_file", "arguments": {"path": "/etc/passwd"}}'

Output:

{
  "toolName": "read_file",
  "isMalicious": true,
  "maliciousProbability": 0.99,
  "threatLevel": "critical",
  "policy": "block",
  "reason": "BLOCKED: High-risk security policy violation detected in tool 'read_file'.",
  "latencyMs": 41
}

📄 License

MIT © Kartik Modi