@polygraphso/mcp

@polygraphso/mcp

MCP server for polygraph.so — independent, lab-evaluated trust grades for MCP servers, exposed as native tools to any MCP client (Claude Desktop, Cursor, and others).

A polygraph is the behavioral trust grade polygraph.so issues for an MCP server: a letter grade (A/B/D/F) from an adversarial litmus test, backed by per-check results, a tool-surface fingerprint, and an evidence URL anyone can re-run. This package lets an agent check the polygraph for a server before recommending or installing it.

Tools

• check_server — look up the published polygraph for a specific MCP server (server_ref like npm/@modelcontextprotocol/server-filesystem). An optional @<version> suffix looks up that exact version.
• list_servers — enumerate every server polygraph has graded, sorted by grade (A first).
• request_grade — add an ungraded server to polygraph's public grading queue. The natural follow-up when check_server returns not_available. Free and best-effort: polygraph runs the litmus test and publishes the grade, which you read later by calling check_server again. No contact details are asked of the agent.

Install in Claude Desktop

Edit claude_desktop_config.json:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json
• Linux: ~/.config/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "polygraph": {
      "command": "npx",
      "args": ["-y", "@polygraphso/mcp"]
    }
  }
}

Restart Claude Desktop. The two polygraph tools appear in the tool picker.

Try it:

Use polygraph to check whether npm/@modelcontextprotocol/server-filesystem is safe to install.

Install in Cursor

Cursor reads MCP servers from ~/.cursor/mcp.json (global) or .cursor/mcp.json (per-project):

{
  "mcpServers": {
    "polygraph": {
      "command": "npx",
      "args": ["-y", "@polygraphso/mcp"]
    }
  }
}

Reload the Cursor window after editing.

Install in any other MCP client

The server speaks stdio. Anything that can launch a stdio MCP server with npx -y @polygraphso/mcp will work. The binary name is polygraphso-mcp if you want to invoke it directly.

Local install

npm i -g @polygraphso/mcp
polygraphso-mcp   # talks JSON-RPC on stdin/stdout

What it returns

check_server({ server_ref: "npm/@modelcontextprotocol/server-filesystem" }) — a graded server:

{
  "status": "graded",
  "polygraph": "A",
  "polygraph_detail": {
    "methodology_version": "litmus-v11",
    "resolved_version": "2.1.0",
    "evidence_url": "https://polygraph.so/mcp/npm/@modelcontextprotocol/server-filesystem"
  }
}

An ungraded server:

{
  "status": "not_available",
  "notify_url": "https://polygraph.so/notify?for=npm/obscure-mcp-server",
  "message": "No published polygraph for npm/obscure-mcp-server yet — treat it as unevaluated. Call request_grade to add it to the public queue, or grade it yourself with the self_grade command.",
  "self_grade": "npx -y -p @polygraphso/litmus polygraphso-litmus litmus npm/obscure-mcp-server"
}

• status is "graded" when a published grade exists, "not_available" otherwise.
• polygraph is the published grade — "A" | "B" | "D" | "F" (no C).
• polygraph_detail carries the per-check results (C-01/C-02/C-03), the tool-surface fingerprint, the methodology version, and resolved_version (the version the grade was run against).
• On not_available: message explains the next steps, self_grade is a one-shot command to grade the server yourself, and notify_url is where a user can subscribe to be notified when the polygraph is published. Call request_grade to add the server to the public queue.

list_servers():

{
  "servers": [
    {
      "server_ref": "npm/@modelcontextprotocol/server-filesystem",
      "polygraph": "A"
    }
  ],
  "total": 75
}

Honest coverage

A server with no polygraph yet is neither safe nor unsafe — it's unevaluated. The tool surfaces this directly; agents using this MCP should pass that distinction through to the user.

Configuration

Env var	Default	Purpose
POLYGRAPH_API_URL	https://polygraph.so	Override the API base, e.g. for local development (http://localhost:3000).

Links

• Site: https://polygraph.so
• CLI: https://www.npmjs.com/package/polygraphso (npx polygraphso check <ref>)
• Source: https://github.com/polygraphso/core
• Issues: https://github.com/polygraphso/core/issues

License

Apache-2.0