polygraph-litmus

polygraph-litmus is an MCP server for Claude Code from polygraphso/litmus. Its token cost is not measured, scanned A, original, Apache-2.0.

A local testing harness and MCP server for checking the behavior of other MCP servers. It tests for tool-output instruction attacks, unwanted data sending, sensitive-data handling, and adversarial inputs, then produces reproducible A–F evidence.

In plain words
What is it for?
It runs behavioral safety tests through a command-line tool or MCP tool and records content-addressed results.
Why use it?
It helps reveal unsafe behavior before an AI agent relies on a third-party MCP server.

MCP server for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: listed in a Claude config.

Part of the polygraph plugin — 1 skill, 2 commands, 1 MCP server shipped together

Good fit It runs behavioral safety tests through a command-line tool or MCP tool and records content-addressed results.

Compare 6 mcp servers from other repositories ↓
Install with agentmods
npx agentmods add mcp/polygraphso/litmus/polygraph-polygraph-litmus
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Clone the repo
git clone --depth 1 https://github.com/polygraphso/litmus

Made for: Claude Code.

Or install polygraph, the plugin that ships this one along with the rest of its 1 skill, 2 commands, 1 MCP server.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for polygraph-litmus

README.md
[![agentmods](https://agentmods.dev/badge/mcp/polygraphso/litmus/polygraph-polygraph-litmus/github.svg)](https://agentmods.dev/mcp/polygraphso/litmus/polygraph-polygraph-litmus)
Your own site
<a href="https://agentmods.dev/mcp/polygraphso/litmus/polygraph-polygraph-litmus"><img src="https://agentmods.dev/badge/mcp/polygraphso/litmus/polygraph-polygraph-litmus/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for polygraph-litmus

Your own site · 80×15
<a href="https://agentmods.dev/mcp/polygraphso/litmus/polygraph-polygraph-litmus"><img src="https://agentmods.dev/badge/mcp/polygraphso/litmus/polygraph-polygraph-litmus.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session not measured What this adds to a session before it is invoked.
When invoked not measured Not applicable: nothing here is loaded into a session.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Security

Grade A, and why

polygraph-litmus scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/polygraph/.mcp.json · 15 lines

What it actually says

{
  "polygraph-litmus": {
    "command": "npx",
    "args": [
      "-y",
      "-p",
      "@polygraphso/[email protected]",
      "polygraphso-litmus-mcp"
    ],
    "env": {
      "POLYGRAPH_API_URL": "https://polygraph.so",
      "NEXT_PUBLIC_POLYGRAPH_NETWORK": "base"
    }
  }
}
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 1mo ago First seen · 15 lines scan A 70e98fa8ea03

Subscribe to this mod's changes

polygraph-litmus is an MCP server published in the GitHub repository polygraphso/litmus (8 stars, last pushed 3mo ago), licensed Apache-2.0. Its token cost is not measured: an MCP server costs its tool schemas, not its config file. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.