litmus — Claude Code MCP server: grade servers A to F
Grades MCP servers and skills using the open behavioral litmus methodology, A to F. Local install runs the full probe suite; hosted endpoint serves lookups only.
claude mcp add --transport http litmus https://polygraph.so/api/mcpWhat litmus does
The server ships six tools. check_server reads a published grade in under a second, no code execution. run_litmus runs the full harness: connects as an agent would, fingerprints the tool surface, runs four probe categories (C-02 needs Docker; without it the grade caps at B), and returns the grade with an evidence bundle on disk. run_skill_litmus grades Claude Code skills with a static scan. list_servers returns servers with published grades, sorted descending. request_grade submits a paid grading request to polygraph.so. verify_attestation reads the onchain proof behind a published grade in EAS on Base.
The hosted endpoint at https://polygraph.so/api/mcp requires no install and serves three lookup tools: check_server, list_servers, request_grade. The stdio variant via npx -y @polygraphso/litmus installs the full toolset, including run_litmus and run_skill_litmus, which execute the target server's code. For Claude Code there is a plugin with two slash commands: /polygraph:grade <server> and /polygraph:check <server>. The repository also includes a GitHub Action polygraphso/litmus@v1 that fails the build when an MCP server or skill grades D or F.
What it helps with
- check an MCP server before install using the open methodology
- grade a server or skill A to F directly from your agent
- list servers with published grades, sorted by quality
- fail a CI build when a dependency grades D or F
- read the blockchain attestation of a published grade on Base
Example prompts for the agent
- Check the grade for
npm/@modelcontextprotocol/server-filesystemin the polygraph.so index - Run the full litmus harness for
github/owner/repoand return the grade with evidence - Show me the first 10 MCP servers with grade A
How to install litmus
1Platform CLI: remote server
claude mcp add --transport http litmus https://polygraph.so/api/mcp2Platform CLI
claude mcp add --env POLYGRAPH_API_URL=<POLYGRAPH_API_URL> --env NEXT_PUBLIC_POLYGRAPH_NETWORK=<NEXT_PUBLIC_POLYGRAPH_NETWORK> --transport stdio litmus -- npx -y @polygraphso/litmusReplace <…> with your own values
1Platform CLI: remote server
codex mcp add litmus --url https://polygraph.so/api/mcp2Platform CLI
codex mcp add litmus --env POLYGRAPH_API_URL=<POLYGRAPH_API_URL> --env NEXT_PUBLIC_POLYGRAPH_NETWORK=<NEXT_PUBLIC_POLYGRAPH_NETWORK> -- npx -y @polygraphso/litmusReplace <…> with your own values
Config file
{
"mcpServers": {
"litmus": {
"url": "https://polygraph.so/api/mcp"
}
}
}{
"mcpServers": {
"litmus": {
"command": "npx",
"args": [
"-y",
"@polygraphso/litmus"
],
"env": {
"POLYGRAPH_API_URL": "<POLYGRAPH_API_URL>",
"NEXT_PUBLIC_POLYGRAPH_NETWORK": "<NEXT_PUBLIC_POLYGRAPH_NETWORK>"
}
}
}
}Replace <…> with your own values
Config file
{
"servers": {
"litmus": {
"type": "http",
"url": "https://polygraph.so/api/mcp"
}
}
}{
"servers": {
"litmus": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"@polygraphso/litmus"
],
"env": {
"POLYGRAPH_API_URL": "<POLYGRAPH_API_URL>",
"NEXT_PUBLIC_POLYGRAPH_NETWORK": "<NEXT_PUBLIC_POLYGRAPH_NETWORK>"
}
}
}
}Replace <…> with your own values
1Platform CLI: remote server
gemini mcp add -t http litmus https://polygraph.so/api/mcp2Platform CLI
gemini mcp add -e POLYGRAPH_API_URL=<POLYGRAPH_API_URL> -e NEXT_PUBLIC_POLYGRAPH_NETWORK=<NEXT_PUBLIC_POLYGRAPH_NETWORK> litmus npx -y @polygraphso/litmusReplace <…> with your own values
Step by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about litmus
How to install litmus in Claude Code?
For the hosted endpoint, run claude mcp add --transport http litmus https://polygraph.so/api/mcp. For the full toolset: `claude mcp add --env POLYGRAPH_API_URL=<POLYGRAPH_API_URL> --env NEXT_PUBLIC_POLYGRAPH_NETWORK=<NEXT_PUBLIC_POLYGRAPH_NETWORK> --transport stdio litmus -- npx -y @polygraphso/litmus. The plugin installs with /plugin marketplace add polygraphso/litmus and /plugin install polygraph@polygraphso`.
What does litmus do?
litmus grades MCP servers and skills using the open behavioral litmus methodology, A to F. The hosted variant looks up published grades in under a second; the stdio variant runs the full harness, executing the target server's code and running four probe categories.
Does litmus require Docker?
Docker is required for the C-02 probe. Without Docker, that probe is skipped and the grade caps at B. The other three probe categories work without Docker.
