dmint-mcp

MCP Proxy Server and Tool Enforcement Gateway for Dmint.

dmint-mcp allows developers to wrap existing Model Context Protocol (MCP) servers with deterministic policy enforcement gates. It intercepts agent tools/call requests over stdio, evaluates Dmint security policy, and routes only authorized calls downstream.

┌─────────────────┐
│    AI Client    │
└────────┬────────┘
         │ stdio (tools/list, tools/call)
         ▼
┌─────────────────────────────────┐
│        Dmint MCP Proxy          │
│                                 │
│  ┌───────────────────────────┐  │
│  │     Enforcement Gate      │  │
│  └─────────────┬─────────────┘  │
└────────────────┼────────────────┘
                 │ stdio (authorized call only)
                 ▼
┌─────────────────────────────────┐
│     Downstream MCP Server       │
└─────────────────────────────────┘

Why This Exists

When using external MCP servers that you cannot modify, dmint-mcp acts as an out-of-process security proxy between the AI agent and the MCP server.

• Tool Discovery Control: Expose or hide tools dynamically from tools/list based on configuration.
• Pre-Call Interception: Intercepts tools/call, maps parameters to a Dmint ToolRequest, and enforces ALLOW, DENY, or APPROVAL_REQUIRED.
• Zero Downstream Leakage: Unapproved or denied calls never reach the downstream MCP server process.
• Approved Retries: Supports Ed25519-signed retry assertion credentials to execute approved workflows over stdio.

Installation

pip install dmint-mcp

Quickstart

import anyio
from dmint_mcp import DmintMCPProxy, MCPIntegrationConfig, MCPToolBinding, DiscoveryMode
from dmint.policy import Policy

# 1. Define integration configuration
config = MCPIntegrationConfig(
    integration_id="sqlite-server",
    command="python3",
    args=["-m", "sqlite_server"],
    tool_bindings=[
        MCPToolBinding(tool_name="read_query", capability="db.read", discovery=DiscoveryMode.EXPOSED),
        MCPToolBinding(tool_name="delete_query", capability="db.delete", discovery=DiscoveryMode.HIDDEN),
    ],
)

# 2. Define policy
policy = Policy.from_mapping({
    "rules": [
        {"effect": "allow", "tool": "db", "action": "read", "resource": "*"},
        {"effect": "deny", "tool": "db", "action": "delete", "resource": "*"},
    ]
})

# 3. Instantiate and run proxy over stdio
proxy = DmintMCPProxy(integration_config=config, policy=policy)

async def main():
    await proxy.serve_stdio()

if __name__ == "__main__":
    anyio.run(main)

Disclosure Modes

Control error disclosure returned to the AI client on denied or approval-required requests:

• DOG (default): Returns structured recovery JSON containing request_id, approval_id, and request_fingerprint.
• GOD: Returns minimal opaque error responses (DMT_403: access denied).
• CAT: Returns structured error codes without revealing internal request fingerprints.

Supported Transports

• Stdio (stdio): Standard input/output process transport for local MCP servers.

Testing

Run the MCP integration and unit test suite:

pytest -v

License

Licensed under the Apache License, Version 2.0. See the LICENSE file for the complete license text.