Litmus MCP Server

litmus

This is the source for @polygraphso/litmus, the open behavioral litmus harness for MCP servers from polygraph.so.

The harness connects to an MCP server the way an agent would, fingerprints its exact tool surface, and runs four probe categories — C-01 tool-output injection (static, dynamic, and second-order — one tool's output weaponized as another's input), C-02 permission/egress (in a hardened default-deny Docker sandbox, matched host and port), C-03 sensitive-data handling (planted canaries), C-04 adversarial-input handling (malformed/oversized and jailbreak inputs) — then grades the server A–F. A passing grade is a measurement, not a guarantee; the methodology and its disclosed limits are at polygraph.so (the open source here is the ground truth).

The same package also grades Claude Code / Agent Skills (a SKILL.md + bundle) under a separate static litmus (litmus-skill-v1): a deterministic byte-scan — S-01 prompt injection, S-03 data-exfiltration instructions, S-04 dangerous commands in bundled scripts — graded A/B/D/F and anchored by a whole-directory content hash, plus a separate advisory quality signal. It is static (no execution): an A is static-clean, not behavioral proof. See packages/litmus/README.md.

The hosted, operator-run grading service is not in this repo — it lives in a separate private repo and consumes this package from npm like any other client.

Layout

This is a pnpm monorepo. Only @polygraphso/litmus is published; the @polygraph/* packages are private building blocks that tsup bundles into it.

packages/
  litmus/          # @polygraphso/litmus — the only published package (lib + 3 bins: CLI, skill CLI, MCP)
  core/            # contract types, canonical JSON, identity helpers
  probes/          # the harness: connect, fingerprint, grade, probe runners, sandbox
  onchain/         # EAS attestation read + encode/decode (Base) — read-only, no minting
  agent/           # agent-gate decision logic + live-fingerprint recheck
  mcp/             # MCP server wrapper
  cli/             # CLI commands + target/auth resolution
  demo-*-mcp/      # demo MCP servers used as test fixtures

See packages/litmus/README.md for the npm-facing usage docs, and polygraph.so for the methodology and proof format.

Develop

pnpm install
pnpm -r typecheck
pnpm -r test
pnpm --filter @polygraphso/litmus build   # → packages/litmus/dist

Release

@polygraphso/litmus is versioned in packages/litmus/package.json. Tag to publish:

git tag litmus-v<x.y.z> && git push origin litmus-v<x.y.z>

The Publish @polygraphso/litmus workflow builds, typechecks, tests, and publishes with npm provenance. See CONTRIBUTING.md for the full process and the local-development workflow for downstream consumers.

License

Apache-2.0 — © polygraph.so.