Configuring Guardrails - Secure MCP Gateway

Overview

Guardrails provide security and content filtering for your MCP servers by validating requests before they reach the server (input guardrails) and responses before they return to the client (output guardrails).

What Are Guardrails?

Guardrails analyze content for:

Input Protection

PII detection & redaction
Injection attack prevention
Toxicity detection
NSFW content filtering
Policy violation detection
Keyword blocking
Bias detection

Output Protection

All input protections
Relevancy validation
Adherence checking
Hallucination detection
PII de-anonymization

Prerequisites

Secure MCP Gateway installed
Enkrypt API key (get from Enkrypt Dashboard)
Server configured in your gateway

Quick Start

Set Enkrypt API Key

First, configure your Enkrypt API key:

secure-mcp-gateway config set-enkrypt-api-key --api-key "your-enkrypt-api-key"

This stores the key in your guardrails configuration at ~/.enkrypt/enkrypt_mcp_config.json:

{
  "plugins": {
    "guardrails": {
      "provider": "enkrypt",
      "config": {
        "api_key": "your-enkrypt-api-key",
        "base_url": "https://api.enkryptai.com"
      }
    }
  }
}

Enable Guardrails for a Server

Using CLI
Using JSON Config
From JSON File

# Enable input guardrails
secure-mcp-gateway config update-server-input-guardrails \
  --config-name "default_config" \
  --server-name "github" \
  --policy '{
    "enabled": true,
    "policy_name": "Sample Airline Guardrail",
    "additional_config": {
      "pii_redaction": true
    },
    "block": [
      "policy_violation",
      "injection_attack",
      "pii",
      "toxicity"
    ]
  }'

# Enable output guardrails
secure-mcp-gateway config update-server-output-guardrails \
  --config-name "default_config" \
  --server-name "github" \
  --policy '{
    "enabled": true,
    "policy_name": "Sample Airline Guardrail",
    "additional_config": {
      "relevancy": true,
      "hallucination": true,
      "adherence": true
    },
    "block": [
      "policy_violation",
      "hallucination"
    ]
  }'

Edit ~/.enkrypt/enkrypt_mcp_config.json:

{
  "mcp_configs": {
    "config-id": {
      "mcp_config": [
        {
          "server_name": "github",
          "input_guardrails_policy": {
            "enabled": true,
            "policy_name": "Sample Airline Guardrail",
            "additional_config": {
              "pii_redaction": true
            },
            "block": [
              "policy_violation",
              "injection_attack",
              "pii",
              "toxicity"
            ]
          },
          "output_guardrails_policy": {
            "enabled": true,
            "policy_name": "Sample Airline Guardrail",
            "additional_config": {
              "relevancy": true,
              "hallucination": true,
              "adherence": true
            },
            "block": [
              "policy_violation",
              "hallucination"
            ]
          }
        }
      ]
    }
  }
}

Create policy files and load them:input_policy.json:

{
  "enabled": true,
  "policy_name": "Sample Airline Guardrail",
  "additional_config": {
    "pii_redaction": true
  },
  "block": [
    "policy_violation",
    "injection_attack",
    "pii"
  ]
}

output_policy.json:

{
  "enabled": true,
  "policy_name": "Sample Airline Guardrail",
  "additional_config": {
    "relevancy": true,
    "hallucination": true,
    "adherence": true
  },
  "block": [
    "policy_violation",
    "hallucination"
  ]
}

Apply them:

secure-mcp-gateway config update-server-guardrails \
  --config-name "default_config" \
  --server-name "github" \
  --input-policy-file "input_policy.json" \
  --output-policy-file "output_policy.json"

Detector Types

Input Detectors

Detector	Description	Block Action
`policy_violation`	Detects content violating custom policies	Blocks request
`injection_attack`	Prevents prompt injection, SQL injection, command injection	Blocks request
`topic_detector`	Flags off-topic requests	Blocks request
`nsfw`	Detects NSFW/adult content	Blocks request
`toxicity`	Identifies toxic, offensive language	Blocks request
`pii`	Finds personally identifiable information	Redacts or blocks
`keyword_detector`	Matches custom keyword blocklist	Blocks request
`bias`	Detects biased or discriminatory content	Blocks request
`sponge_attack`	Prevents resource exhaustion attacks	Blocks request
`system_prompt_protection`	Protects against prompt leaking	Blocks request
`copyright_protection`	Detects copyrighted content	Blocks request

Output Detectors

Detector	Description	Block Action
All input detectors	Same as above	Blocks response
`relevancy`	Validates response relevance to input	Blocks if irrelevant
`adherence`	Checks if response follows instructions	Blocks if non-adherent
`hallucination`	Detects fabricated information	Blocks response

PII Detection & Redaction

Enabling PII Redaction

Enable in input guardrails

{
  "input_guardrails_policy": {
    "enabled": true,
    "policy_name": "PII Protection Policy",
    "additional_config": {
      "pii_redaction": true
    },
    "block": ["pii"]
  }
}

PII is detected and redacted

Input: "My email is [email protected] and SSN is 123-45-6789"Redacted: "My email is [PII_EMAIL_1] and SSN is [PII_SSN_1]"

Response is de-anonymized

The gateway automatically restores PII in the response using the mapping created during redaction.

How PII Redaction Works

Custom Policies

Creating a Policy in Enkrypt Dashboard

Navigate to Policies

Go to Enkrypt Guardrails

Create New Policy

Click “Create Policy” and name it (e.g., “Production API Policy”)

Configure Detectors

Select which detectors to enable and their thresholds:

Injection Attack: Threshold 0.7, Action: Block
Toxicity: Threshold 0.6, Action: Warn
PII: Always detect, Action: Redact
Keywords: Add custom blocked terms

Save and Use

Save the policy and reference it in your config:

{
  "policy_name": "Production API Policy"
}

Example: Strict Security Policy

{
  "enabled": true,
  "policy_name": "Strict Security Policy",
  "additional_config": {
    "pii_redaction": true,
    "content_filtering": true
  },
  "block": [
    "policy_violation",
    "injection_attack",
    "toxic_content",
    "nsfw",
    "pii",
    "keyword_detector",
    "bias",
    "sponge_attack",
    "system_prompt_protection"
  ]
}

Example: Lenient Development Policy

{
  "enabled": true,
  "policy_name": "Development Policy",
  "additional_config": {
    "pii_redaction": false
  },
  "block": [
    "injection_attack",
    "pii"
  ]
}

Advanced Configuration

Async Guardrails

Enable asynchronous guardrail processing for improved performance:

{
  "common_mcp_gateway_config": {
    "enkrypt_async_input_guardrails_enabled": true,
    "enkrypt_async_output_guardrails_enabled": true
  }
}

Async guardrails process in the background and don’t block requests. Use only for logging/monitoring, not for blocking malicious content.

Guardrail Timeouts

Configure timeout settings in the common config:

{
  "common_mcp_gateway_config": {
    "timeout_settings": {
      "guardrail_timeout": 15,
      "escalation_policies": {
        "warn_threshold": 0.8,
        "timeout_threshold": 1.0,
        "fail_threshold": 1.2
      }
    }
  }
}

Per-Tool Guardrails

Apply guardrails to specific tools only:

{
  "server_name": "filesystem",
  "tool_guardrails_policy": {
    "enabled": true,
    "policy_name": "File Operations Policy",
    "block": [
      "injection_attack",
      "policy_violation"
    ]
  },
  "tools": {
    "write_file": {"enabled": true},
    "delete_file": {"enabled": false}
  }
}

Testing Guardrails

Test Input Guardrails

Ask Claude to:
"Use the GitHub server to search for repositories containing my SSN: 123-45-6789"

# Expected: Request blocked or PII redacted

Test Output Guardrails

Ask Claude to:
"Make up a fictional story about how GitHub was founded, then search for it"

# Expected: Hallucination detector blocks fabricated response

Check Guardrail Logs

Guardrail detections are logged in the gateway logs:

# macOS
tail -f ~/Library/Logs/Claude/mcp*.log | grep -i "guardrail"

# Windows
Get-Content "$env:APPDATA\Claude\logs\mcp*.log" -Wait | Select-String "guardrail"

Look for entries like:

[INFO] Input guardrail detected violation: injection_attack (severity: 0.95)
[WARN] Request blocked by policy: Strict Security Policy
[INFO] PII redacted: 2 email addresses, 1 SSN

Monitoring & Metrics

View Guardrail Activity

In Claude Desktop, ask:

Show me the cache status and recent guardrail activity

Or use the CLI:

secure-mcp-gateway system health-check

Enkrypt Dashboard

View detailed guardrail analytics in the Enkrypt Dashboard:

Request/block rates
Top violations
PII detection trends
Policy effectiveness

Use Cases

Financial Services

Protect sensitive financial data:

{
  "policy_name": "Financial Compliance Policy",
  "additional_config": {
    "pii_redaction": true
  },
  "block": [
    "pii",
    "injection_attack",
    "policy_violation",
    "sensitive_data"
  ]
}

Detects and redacts:

Credit card numbers
SSNs
Account numbers
Tax IDs

Healthcare (HIPAA)

Ensure HIPAA compliance:

{
  "policy_name": "HIPAA Compliance Policy",
  "additional_config": {
    "pii_redaction": true,
    "phi_protection": true
  },
  "block": [
    "pii",
    "policy_violation",
    "injection_attack"
  ]
}

Protects:

Patient names
Medical record numbers
Health information
Insurance IDs

Education

Protect student data (FERPA):

{
  "policy_name": "Student Data Protection",
  "additional_config": {
    "pii_redaction": true
  },
  "block": [
    "pii",
    "nsfw",
    "toxicity",
    "bias"
  ]
}

Code Development

Prevent code injection:

{
  "policy_name": "Code Security Policy",
  "block": [
    "injection_attack",
    "policy_violation",
    "system_prompt_protection"
  ]
}

Troubleshooting

Guardrails Not Working

Verify API Key

secure-mcp-gateway config get-enkrypt-api-key

Ensure it matches your key from Enkrypt Dashboard

Check Policy Exists

Log into Enkrypt Dashboard and verify the policy name exists in your account

Confirm Guardrails Enabled

secure-mcp-gateway config get-server \
  --config-name "config" \
  --server-name "server"

Look for "enabled": true in guardrails policies

Test Connectivity

curl -H "Authorization: Bearer YOUR_ENKRYPT_API_KEY" \
  https://api.enkryptai.com/guardrails/health

False Positives

Adjust thresholds: Lower detector sensitivity in Enkrypt Dashboard
Whitelist terms: Add exceptions to keyword detector
Refine policy: Use more specific detectors instead of broad ones

Performance Issues

Enable async guardrails: For non-blocking operation
Increase timeout: Adjust guardrail_timeout in config
Cache policies: Guardrail results are cached by default
Use fewer detectors: Only enable necessary protections

Best Practices

Start Lenient

Begin with minimal detectors and add more based on observed threats

Test Thoroughly

Test guardrails in development before production deployment

Monitor Metrics

Review Enkrypt Dashboard regularly for policy effectiveness

Different Policies per Environment

Use strict policies in production, lenient in development

Enable PII Redaction

Always enable PII redaction for servers handling sensitive data

Document Policies

Keep a record of which policies are used where and why

Next Steps

OAuth Setup

Secure remote servers with OAuth authentication

External Cache

Improve guardrail performance with Redis caching

Custom Plugins

Create custom guardrail providers

API Reference

Explore guardrails API endpoints

Get Started

Core Concepts

Features

Deployment

Client Integration

Observability

Security

Guides

​Overview

​What Are Guardrails?

Input Protection

Output Protection

​Prerequisites

​Quick Start

​Set Enkrypt API Key

​Enable Guardrails for a Server

​Detector Types

​Input Detectors

​Output Detectors

​PII Detection & Redaction

​Enabling PII Redaction

​How PII Redaction Works

​Custom Policies

​Creating a Policy in Enkrypt Dashboard

​Example: Strict Security Policy

​Example: Lenient Development Policy

​Advanced Configuration

​Async Guardrails

​Guardrail Timeouts

​Per-Tool Guardrails

​Testing Guardrails

​Test Input Guardrails

​Test Output Guardrails

​Check Guardrail Logs

​Monitoring & Metrics

​View Guardrail Activity

​Enkrypt Dashboard

​Use Cases

​Troubleshooting

​Guardrails Not Working

​False Positives

​Performance Issues

​Best Practices

Start Lenient

Test Thoroughly

Monitor Metrics

Different Policies per Environment

Enable PII Redaction

Document Policies

​Next Steps

OAuth Setup

External Cache

Custom Plugins

API Reference

Build docs developers (and LLMs) love

Overview

What Are Guardrails?

Prerequisites

Quick Start

Set Enkrypt API Key

Enable Guardrails for a Server

Detector Types

Input Detectors

Output Detectors

PII Detection & Redaction

Enabling PII Redaction

How PII Redaction Works

Custom Policies

Creating a Policy in Enkrypt Dashboard

Example: Strict Security Policy

Example: Lenient Development Policy

Advanced Configuration

Async Guardrails

Guardrail Timeouts

Per-Tool Guardrails

Testing Guardrails

Test Input Guardrails

Test Output Guardrails

Check Guardrail Logs

Monitoring & Metrics

View Guardrail Activity

Enkrypt Dashboard

Use Cases

Troubleshooting

Guardrails Not Working

False Positives

Performance Issues

Best Practices

Next Steps