MCP Proxy

The MCP Proxy is a transparent stdin/stdout proxy that sits between an MCP client (Claude Desktop, etc.) and any MCP server. It intercepts every tool call and provides cryptographic audit trails, risk scoring, and policy enforcement — without modifying the server or client.

Repository: mcp-proxy/

Features

• Risk scoring — scores every tool call 0-100 based on operation type, sensitive keywords, and patterns
• Operation classification — classifies calls as read, write, delete, or execute by tool name
• Policy enforcement — YAML rules engine with four actions: pass, flag, pause (approval required), and block
• Approval workflows — HTTP endpoints for async approval of paused operations
• Cryptographic receipts — Ed25519-signed W3C Verifiable Credentials, hash-chained per session
• Intent tracking — groups related tool calls by temporal proximity
• Data redaction — JSON-aware and pattern-based redaction of secrets before storage
• Encryption at rest — optional AES-256-GCM encryption of audit data
• Audit CLI — list, inspect, verify, export, and query receipts from the command line

How it works

MCP Client (Claude)
    |
    v
 mcp-proxy (stdin/stdout)
    |  - classify operation
    |  - score risk
    |  - evaluate policy rules
    |  - redact sensitive data
    |  - sign receipt
    |  - log to SQLite
    v
 MCP Server (any)

The proxy reads JSON-RPC messages on stdin, processes tools/call requests, forwards them to the wrapped server, and returns the response. Each tool call generates a signed Agent Receipt that is hash-chained into a tamper-evident audit log.

Quick start

# Install
go install github.com/agent-receipts/ar/mcp-proxy/cmd/mcp-proxy@latest

# Wrap any MCP server
mcp-proxy node /path/to/mcp-server.js

# With configuration
mcp-proxy \
  --name github \
  --key private.pem \
  --rules rules.yaml \
  --taxonomy taxonomy.json \
  node /path/to/github-mcp-server.js

Claude Desktop integration

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "github-audited": {
      "command": "mcp-proxy",
      "args": [
        "--name", "github",
        "node", "/path/to/github-mcp-server.js"
      ]
    }
  }
}

See Installation to get started, or Configuration for the full set of options.