Introduction

What is open-mcp-guardrails?

A policy-based guardrails proxy that sits in front of any MCP server.

It scans both arguments and outputs of tool calls, detecting and blocking content that violates your policies.

Features

PII & Secret Protection

Automatically detects and blocks sensitive information like email addresses, phone numbers, credit card numbers, API keys, and tokens from leaking between tools.

Flow Control

Controls dangerous tool call patterns like web fetch → email send, preventing unintended data exfiltration.

Prompt Injection Detection

Detects and blocks prompt injection attacks using scoring-based heuristics.

Zero-Config Start

Just call defineConfig() with no arguments to enable PII + secret protection by default. Customize rules as needed.

Next Steps

• Installation — Install via npm
• Quick Start — Create your first config file