mcpshield 0.2.3

MCPShield - Secure access for AI agents with deterministic policy enforcement

MCPShield

Secure PostgreSQL access for AI agents with deterministic policy enforcement and comprehensive auditing.

Features

• MCP Server: Claude Code compatible stdio protocol
• PostgreSQL Tools: Safe, policy-enforced database access
• Fail-Closed Policy Engine: YAML-based security rules with default deny
• Centralized Policy Management: Policies authored in dashboard, automatically synced
• Audit Trail: Complete event logging to MCPShield control plane with policy_hash tracking
• Event Spooling: Never lose audit events, even when offline
• Developer-Friendly: Clear logs, helpful errors, easy configuration

Quick Start

Installation

pip install mcpshield

Super Quick Setup (Interactive)

The easiest way to get started:

mcpshield init

This interactive wizard will:

• Configure your PostgreSQL connection
• Set up your MCPShield API key
• Automatically integrate with Claude Code and/or Cursor
• Test your configuration

Setup (Environment Variables - Recommended)

No configuration file needed! Just set environment variables and run.

1. Create project and policy in MCPShield dashboard:

   • Go to https://app.mcpshield.xyz
   • Create project → Get Project ID
   • Create policy → Define security rules
   • Create API key

2. Set environment variables:

   macOS/Linux:

   export PG_DSN="postgresql://user:pass@localhost:5432/dbname"
   export MCPSHIELD_API_KEY="mcps_your_key"
   export PROJECT_ID="proj_your_id"
   export API_BASE_URL="https://api.mcpshield.xyz"  # Optional, this is the default
   

   Windows (PowerShell):

   $env:PG_DSN = "postgresql://user:pass@localhost:5432/dbname"
   $env:MCPSHIELD_API_KEY = "mcps_your_key"
   $env:PROJECT_ID = "proj_your_id"
   $env:API_BASE_URL = "https://api.mcpshield.xyz"  # Optional, this is the default
   

   Or use a .env file:

   # .env
   PG_DSN=postgresql://user:pass@localhost:5432/dbname
   MCPSHIELD_API_KEY=mcps_your_key
   PROJECT_ID=proj_your_id
   API_BASE_URL=https://api.mcpshield.xyz
   POLICY_SOURCE=remote
   

3. Verify setup:

   mcpshield doctor
   
   # Or with .env file:
   mcpshield doctor --env-file .env
   

4. Run the gateway:

   mcpshield serve
   
   # Or with .env file:
   mcpshield serve --env-file .env
   

Setup (YAML Config - Optional)

For advanced users who prefer a configuration file, you can create mcpshield.yaml:

database:
  dsn: null  # Set via PG_DSN env var

api:
  base_url: "https://api.mcpshield.xyz"
  project_id: null  # Set via PROJECT_ID env var
  api_key: null  # Set via MCPSHIELD_API_KEY env var

policy:
  source: "remote"
  refresh_seconds: 60

# Optional: local policy file for fallback
# policy:
#   source: "remote_with_fallback"
#   file: "policy.yaml"

Then run with --config:

mcpshield doctor --config mcpshield.yaml
mcpshield serve --config mcpshield.yaml

Claude Code Integration

Add to your Claude Code MCP configuration (~/.claude/mcp.json):

Option 1: Environment Variables Only (Recommended)

{
  "mcpServers": {
    "mcpshield": {
      "command": "mcpshield",
      "args": ["serve"],
      "env": {
        "PG_DSN": "postgresql://user:pass@localhost:5432/db",
        "MCPSHIELD_API_KEY": "mcps_...",
        "PROJECT_ID": "proj_...",
        "API_BASE_URL": "https://api.mcpshield.xyz"
      }
    }
  }
}

Option 2: With .env File

{
  "mcpServers": {
    "mcpshield": {
      "command": "mcpshield",
      "args": ["serve", "--env-file", "/path/to/.env"]
    }
  }
}

Option 3: With YAML Config

{
  "mcpServers": {
    "mcpshield": {
      "command": "mcpshield",
      "args": ["serve", "--config", "/path/to/mcpshield.yaml"],
      "env": {
        "PG_DSN": "postgresql://user:pass@localhost:5432/db",
        "MCPSHIELD_API_KEY": "mcps_...",
        "PROJECT_ID": "proj_..."
      }
    }
  }
}

How Policy Synchronization Works

┌──────────────────────────────────────────────────────────────┐
│                     MCPShield Dashboard                      │
│                                                              │
│  1. Author policy in UI                                      │
│  2. Save policy (stored in database)                         │
│  3. policy_hash computed (SHA-256)                           │
└──────────────────────────┬───────────────────────────────────┘
                           │
                           │ GET /projects/{id}/policy
                           │
                           ▼
                  ┌────────────────────┐
                  │  MCPShield Gateway │
                  │                    │
                  │  On startup:       │
                  │  • Fetch policy    │
                  │  • Cache locally   │
                  │  • Compute hash    │
                  │                    │
                  │  Every 60s:        │
                  │  • Re-fetch policy │
                  │  • Update cache    │
                  │  • Update hash     │
                  └────────────────────┘
                           │
                           │ Every request includes:
                           │ • decision (allow/deny)
                           │ • policy_hash
                           │
                           ▼
                  ┌────────────────────┐
                  │   Audit Events     │
                  │                    │
                  │  {                 │
                  │    decision: allow │
                  │    policy_hash:... │
                  │  }                 │
                  └────────────────────┘

Configuration

Environment Variables

MCPShield supports configuration via environment variables (no YAML file required):

Required:

• PG_DSN or DATABASE_URL - PostgreSQL connection string
• PROJECT_ID - Your MCPShield project ID
• MCPSHIELD_API_KEY - Your MCPShield API key

Optional:

• API_BASE_URL - API endpoint (default: https://api.mcpshield.xyz)
• POLICY_SOURCE - Policy source: remote, remote_with_fallback, or local (default: remote)
• POLICY_FILE - Path to local policy file (for fallback)
• POLICY_REFRESH_SECONDS - Policy refresh interval (default: 60)
• SPOOL_DIR - Event spool directory (default: ~/.mcpshield/spool)
• POLICY_CACHE_DIR - Policy cache directory (default: ~/.mcpshield/cache)
• LOG_LEVEL - Logging level: DEBUG, INFO, WARNING, ERROR (default: INFO)
• LOG_DECISIONS - Log policy decisions: true or false (default: true)
• BATCH_SIZE - Event batch size (default: 10)
• BATCH_TIMEOUT - Event batch timeout in seconds (default: 5)

Policy Source Options

remote (Recommended - Default):

• Fetches policy from MCPShield API only
• No local policy file needed
• Fails if API unreachable (fail-closed)
• Always uses latest policy from dashboard
• Policy cached locally at ~/.mcpshield/cache/policy.yaml

remote_with_fallback:

• Tries API first
• Falls back to cached policy if API fails
• Falls back to local file if cache unavailable
• Provides resilience during API outages

local:

• Uses local policy file only
• No API calls
• Useful for offline development
• Requires POLICY_FILE to be set

Fail-Closed Behavior

Gateway WILL NOT start if:

• Policy source is remote and API is unreachable (and no cache exists)
• Policy source is remote_with_fallback and ALL of: API fails, no cache, no local file
• This ensures gateway never operates without a policy

Documentation

• User Guide: https://mcpshield.xyz/docs
• Policy Syntax: https://mcpshield.xyz/docs/policy
• Troubleshooting: https://mcpshield.xyz/docs/troubleshooting

Security

MCPShield is designed with security-first principles:

• Default Deny: All operations blocked unless explicitly allowed
• Read-Only Enforcement: Blocks destructive SQL keywords
• Schema Validation: Only access allowed tables
• Data Redaction: Remove sensitive data (emails, phones) from results
• Rate Limiting: Enforce query limits and timeouts
• Audit Everything: Complete audit trail with policy_hash tracking

CLI Commands

# Run the gateway (env vars only)
mcpshield serve

# Run the gateway (with .env file)
mcpshield serve --env-file .env

# Run the gateway (with YAML config)
mcpshield serve --config mcpshield.yaml

# Validate configuration
mcpshield validate
mcpshield validate --env-file .env
mcpshield validate --config mcpshield.yaml

# Run diagnostics
mcpshield doctor
mcpshield doctor --env-file .env
mcpshield doctor --config mcpshield.yaml

# Get version
mcpshield --version

Support

• Documentation: https://mcpshield.xyz/docs
• Issues: Report via MCPShield support channels

License

MIT License - see LICENSE file for details