Proxy Rules

The mcp-scanner proxy intercepts tool calls between AI clients and MCP servers, applying rules for filtering and rate limiting.

Setting Up the Proxy

1. Update Client Configuration

Replace the server command with mcp-scanner proxy:

Before:

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/"]
    }
  }
}

After:

{
  "mcpServers": {
    "filesystem": {
      "command": "mcp-scanner",
      "args": ["proxy", "--server", "npx -y @modelcontextprotocol/server-filesystem /"]
    }
  }
}

2. Configure Rules

Rules can be configured via the web dashboard (mcp-scanner serve) or the API.

Rule Types

Block Rules

Prevent specific tools from being called:

{
  "rule_type": "block",
  "pattern": "delete_*",
  "reason": "Prevent destructive operations"
}

Rate Limit Rules

Limit how often a tool can be called:

{
  "rule_type": "rate_limit",
  "pattern": "send_email",
  "max_calls": 10,
  "window_seconds": 3600,
  "reason": "Limit email sending"
}

Pattern Matching

Rules use glob patterns:

Rule Priority

Rules are evaluated in priority order (lower numbers first). The first matching rule is applied.

Audit Logging

All proxied tool calls are logged to the SQLite database, including:

• Timestamp
• Server name
• Tool name and arguments
• Result or error
• Whether the call was blocked
• Execution duration