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MCP Guard

Tool-level security for Model Context Protocol servers.

MCP Guard provides trust badges and identity verification for Model Context Protocol (MCP) tool calls, implementing:

  • RFC-006: MCP Tool Authority and Evidence
  • RFC-007: MCP Server Identity Disclosure and Verification

Why MCP Guard?

MCP servers expose powerful tools to autonomous agents—file systems, databases, APIs. But MCP itself doesn't define how to:

  • Authenticate which agent is calling a tool
  • Authorize whether that agent should have access
  • Audit what happened for post-incident review
  • Identify which server the client is connecting to

MCP Guard solves this with:

Feature Description
@guard decorator Protect tools with trust-level requirements
Evidence logging Cryptographic audit trail for every invocation
Server identity Verify MCP servers before connecting
Server registration Generate keypairs and register server DIDs
Trust levels 0 (self-signed) → 4 (extended validation)

Quick Example

Server-Side (Protect Your Tools)

from capiscio_mcp import guard

@guard(min_trust_level=2)
async def read_database(query: str) -> list[dict]:
    """Only agents with Trust Level 2+ can execute this tool."""
    pass

Client-Side (Verify Servers)

from capiscio_mcp import verify_server, ServerState

result = await verify_server(
    server_did="did:web:mcp.example.com",
    server_badge="eyJhbGc...",
    transport_origin="https://mcp.example.com",
)

if result.state == ServerState.VERIFIED_PRINCIPAL:
    print(f"Trusted server at Level {result.trust_level}")

Trust Levels

Per RFC-002 v1.4:

Level Name Validation Use Case
0 Self-Signed (SS) None, did:key issuer Local dev, testing, demos
1 Registered (REG) Account registration Development, internal agents
2 Domain Validated (DV) DNS/HTTP challenge Production, B2B agents
3 Organization Validated (OV) DUNS/legal entity High-trust production
4 Extended Validated (EV) Manual review + legal Regulated industries

Next Steps

  • Installation

    Install capiscio-mcp and configure your environment.

    Installation

  • Quickstart

    Get started in 5 minutes with the @guard decorator.

    Quickstart

  • Server Registration

    Generate a keypair and register your server's DID.

    Server Registration

  • Server-Side Guide

    Protect your MCP tools with trust-level requirements.

    Server-Side

  • Client-Side Guide

    Verify MCP server identity before connecting.

    Client-Side

Documentation