mcpbeat

Litmus MCP Server

io.github.polygraphso/litmus
not responding

Litmus is listed as active in the registry but did not answer our last check. 188 installs a week from npm. It exposes 3 tools. Last commit 20 Jul 2026.

Grade MCP servers A to F with the open behavioral litmus. npm: full toolset; hosted: lookups only.

Installs per day peak 583 · avg 97 · -71% w/w
a month agotoday
Uptime history 41 hours of history · worst hour 0%
41 hours agonow
22.0%
Uptime 24h
20 of 91 checks
3
Tools
read from the server
502 ms
Response time
average over 24h
188
Installs / week
npm and PyPI

Connect this server

Endpoint below is the one we actually reach during checks — not the one copied from a README. Last verified 8 min ago.

run in your terminal
claude mcp add litmus --transport http https://polygraph.so/api/mcp
~/Library/Application Support/Claude/claude_desktop_config.json
{
  "mcpServers": {
    "litmus": {
      "url": "https://polygraph.so/api/mcp"
    }
  }
}
~/.codex/config.toml
[mcp_servers.litmus]
url = "https://polygraph.so/api/mcp"
.cursor/mcp.json
{
  "mcpServers": {
    "litmus": {
      "url": "https://polygraph.so/api/mcp"
    }
  }
}
.vscode/mcp.json
{
  "mcpServers": {
    "litmus": {
      "url": "https://polygraph.so/api/mcp"
    }
  }
}

Available tools 3

Read directly from the server with tools/list, grouped by what they act on. If a tool disappears, we record the date.

request
request_grade
Record a grade request with polygraph.so. Recording is free; only real, plausibly-MCP targets are accepted. Grading starts once the request's one-time $1 USD fee is paid: payment.payUrl is the human/browser checkout (paid in $POLYGRAPH), and payment.x402Url is the agent rail, POST the same request body there with an x402-capable client. A bare POST to x402Url returns a 402 with the exact payment requirements; retry with an X-PAYMENT header. Asset is USDC on Base mainnet (eip155:8453). On the x402 rail settlement is deferred: the authorization is charged only once a grade lands, and a run the harness cannot complete voids it, so nothing is charged. Paying starts a 48h grading clock. The fee buys the run, never the grade. After paying, poll check_server with the same server_ref for the published result, or poll statusUrl for progress.
server
check_server
Read a server's published behavioral grade (A-F) from polygraph.so in under a second; no execution. The pre-flight check before recommending or installing an MCP server. On a miss it returns not_available (unevaluated: neither safe nor unsafe) with next steps.
servers
list_servers
Servers with a published polygraph grade, sorted A-first then by ref. Returns up to `limit` rows starting at `offset` (default limit 25, capped at 100 per call); `grade` restricts to one letter. `summary` always covers the full graded corpus (a total plus a count per grade), regardless of `grade`, `limit`, or `offset`.

Endpoints

URLTransportStateLatencyChecked
https://polygraph.so/api/mcp streamable-http answering 43 ms 8 min ago

Litmus — questions

Answers built from our own checks of this server.

What can Litmus do?
It exposes 3 tools, read directly from the server on our last check. Among them: check_server, list_servers, request_grade. The full list with descriptions is on this page — we take it from the server itself via tools/list, not from a README. How MCP servers expose tools in the first place →
Is Litmus working right now?
We send a real MCP handshake every 15 minutes. Over the last 24 hours 20 of 91 checks got a reply (22.0%), average response time 502 ms. The bar chart above shows every period we have measured.
The registry lists Litmus as active — why does it not respond?
The official MCP registry stores what the author submitted; it does not verify that the server still runs. We check the endpoint ourselves, and this one does not answer. Catalogues that copy the registry without checking will show it as working.
How do I connect Litmus?
Copy the ready config from this page — we generate it for Claude Code, Claude Desktop, Codex, Cursor and VS Code, each with the file path that client actually reads. It is a remote server, so there is nothing to install — the client connects to the address.
Does Litmus need an API key?
No. Litmus completed a full MCP handshake with us as an anonymous client and listed its tools without asking for anything. All 3 of them are readable on this page. This is what we observed, not what the docs claim.
How fast is Litmus?
It answers our handshake in 502 ms on average, which is faster than 22% of all working MCP servers we measure. That is on the slow side — worth knowing if the tool sits inside an interactive loop. The comparison comes from our own checks across the whole registry, every 15 minutes.
How many people use Litmus?
The npm package @polygraphso/litmus was installed 188 times in the last week. Week over week that is -71%. We show installs rather than GitHub stars on purpose: a star is a bookmark, an install is someone actually running it.
Is Litmus open source?
Yes — it is published under the Apache-2.0 licence, written in TypeScript and 7 stars on GitHub. The source link is on this page, so you can read exactly what it does with your data before you connect it.