@jamjet/mcp-shim

JamJet policy + audit + approval as an MCP stdio interceptor. Drop-in between any MCP client (Claude Desktop, Cursor, OpenAI Agents SDK with MCP, custom) and any MCP server. One policy file, every tools/call governed.

Install + wire in Claude Desktop

In claude_desktop_config.json (or ~/.config/claude-code/...):

{
  "mcpServers": {
    "postgres": {
      "command": "npx",
      "args": [
        "-y", "@jamjet/mcp-shim",
        "--policy", "~/.jamjet/policy.yaml",
        "--server", "postgres",
        "--",
        "postgres-mcp", "--db", "postgresql://localhost/mydb"
      ]
    }
  }
}

Same shape works for Cursor, OpenAI Agents SDK MCP clients, any stdio-launched MCP server.

See it in 60 seconds

mkdir -p ~/.jamjet
cat > ~/.jamjet/policy.yaml <<'EOF'
version: 1
rules:
  - { match: "*delete*", action: block }
  - { match: "*drop*", action: block }
  - { match: "shell.exec", action: block }
EOF

Restart Claude Desktop. Any tools/call matching *delete* from any MCP tool gets a JSON-RPC policy error back to the client — and the real MCP server never sees the request.

What you get

• Block unsafe MCP tools at the wire — before the real MCP server is invoked
• Approve risky tools via jamjet approve <run-id> (approval flow lands with @jamjet/cli in v0.2)
• Audit JSONL at ~/.jamjet/audit/<YYYY-MM-DD>/mcp-shim.jsonl

Same policy, other places

The same policy.yaml is consumed by:

• Claude Code PreToolUse hook via @jamjet/claude-code-hook
• OpenAI Agents SDK guardrail via @jamjet/openai-guardrail (coming next)
• JamJet Python SDK via jamjet on PyPI
• JamJet TS SDK via @jamjet/cloud on npm

Write the safety policy once. Run it everywhere your agents can act.

License

Apache-2.0