# litmus MCP server

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

## Links
- Registry page: https://www.getdrio.com/mcp/io-github-polygraphso-litmus
- Repository: https://github.com/polygraphso/litmus
- Website: https://polygraph.so

## Install
- Command: `npx -y @polygraphso/litmus`
- Endpoint: https://polygraph.so/api/mcp
- Auth: Not captured

## Setup notes
- Package: Npm @polygraphso/litmus v0.36.0
- Environment variable: POLYGRAPH_API_URL (default https://polygraph.so)
- Environment variable: NEXT_PUBLIC_POLYGRAPH_NETWORK (default base)
- Remote endpoint: https://polygraph.so/api/mcp

## Tools
- check_server (Check a server's published polygraph grade) - 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. Endpoint: https://polygraph.so/api/mcp
- list_servers (List servers with a published grade) - 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`. Endpoint: https://polygraph.so/api/mcp
- request_grade (Request a polygraph grade for an MCP server) - 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. Endpoint: https://polygraph.so/api/mcp

## Resources
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## Prompts
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## Metadata
- Owner: io.github.polygraphso
- Version: 0.36.0
- Runtime: Npm
- Transports: STDIO, HTTP
- License: Not captured
- Language: Not captured
- Stars: Not captured
- Updated: Jul 20, 2026
- Source: https://registry.modelcontextprotocol.io