Pkgtruth MCP Server

pkgtruth

Ground truth about npm packages, for AI coding agents and CI.

Your agent just wrote npm install unused-imports. That package is not the linter plugin it meant. It is a name an attacker registered because models kept inventing it — and npm has since replaced it with a security placeholder.

pkgtruth catches that before it reaches your lockfile.

Why this exists

Large language models invent package names. Measured across models, 19.7% of generated package names were hallucinated, and when researchers re-ran the prompts, 43% of those names came back every single time.

That reproducibility is the whole attack. An attacker does not need to compromise a maintainer, poison a build server, or find a vulnerability. They watch what models invent, register the name, and wait. The technique is called slopsquatting, and it is already happening in the wild.

The standing security advice is that agents with package-management capabilities should not install anything without a review gate. pkgtruth is that gate, in a form an agent can call on its own.

Install

As an MCP server (for coding agents)

{
  "mcpServers": {
    "pkgtruth": {
      "command": "npx",
      "args": ["-y", "pkgtruth"]
    }
  }
}

Two tools become available:

As a CLI (for humans and CI)

npx pkgtruth check express unused-imports
npx pkgtruth scan .

scan reads every dependency in a package.json and exits non-zero when something is blocking, so it drops straight into CI:

- name: Block hallucinated and slopsquatted dependencies
  run: npx pkgtruth scan . --fail-on danger

What it checks

Verdicts are SAFE, CAUTION, DANGER, HALLUCINATED, or UNKNOWN. Every one arrives with the evidence behind it — an agent should never have to take "DANGER" on faith, and neither should you.

Design notes

Network failures never open the gate. If the registry is unreachable, the verdict is UNKNOWN, never SAFE. A degraded network must not silently turn a security check into a no-op.

Popular packages are not flagged. Checked against a real 18-dependency project, zero false positives. A gate that cries wolf gets switched off.

No build step. Two direct dependencies — the MCP SDK and zod, both only needed for the server. npx pkgtruth starts immediately.

Limitations

Read these before trusting it:

• npm only. PyPI, crates.io, and Go modules are not covered yet.
• Registry metadata only. It does not analyze package source code, so a legitimate-looking package with a malicious payload can still pass.
• Not a replacement for npm audit or Snyk. Those find known CVEs in code you already trust. pkgtruth asks the earlier question: should this package be here at all?
• New legitimate packages will get CAUTION. That is deliberate. Newness genuinely is a risk signal; use --fail-on danger so it does not block.

Options

--json              Machine-readable output
--fail-on <level>   danger (default) | caution

--fail-on caution also blocks packages that could not be verified at all, since "we could not check" is not a pass.

Exit codes: 0 clean, 1 blocking packages found, 2 usage or runtime error.

Configuration

On speed and rate limits

Adoption figures come from npm's downloads API, which throttles bursts and cannot batch scoped names — a project with several @scope/pkg dependencies would spend its whole budget on every scan.

Three things keep that in check: the bulk endpoint resolves all unscoped names in one request, requests to that host are paced serially, and figures are cached on disk for six hours. Weekly download counts move slowly, so a six-hour-old number is no less true.

A warm scan of ~18 dependencies takes about 1.4 seconds. A cold one after heavy use may return UNKNOWN for some packages — that is the intended failure mode. A throttled lookup never becomes SAFE; re-run, and the cache will answer.

Cached figures are keyed by the API they came from, so pointing PKGTRUTH_DOWNLOADS_API at a private registry never reuses npm's numbers.

Contributing

Issues and pull requests are welcome at github.com/hxckya/pkgtruth.

Two things make a report especially useful: a legitimate package that gets flagged, and a malicious one that slips through. Both are regression tests waiting to be written.

npm test                 # offline
npm run test:online      # includes live registry checks

License

MIT © hxckya