A postinstall script runs on every npm install, on every developer machine and CI server. This skill flags install scripts that download code, dependencies fetched over plain http, tokens written into config, and six other package.json and .npmrc risks, and tells you how to fix each one.

Your agent runs a scanner on the project (npm, yarn, pnpm or bun, monorepos included; node_modules is skipped). It returns BLOCK, REVIEW, or NOT FLAGGED, with the file, line, reason, and a safer approach.

What it checks

BLOCK (fix before shipping)

• N01: a preinstall, install, postinstall or prepare script that downloads from the network

• N02: a dependency fetched over plain http://

• N03: an npm or GitHub token written in package.json or .npmrc

REVIEW (check before release)

• N10: a package.json that is not valid JSON

• N11: a *, latest, empty or open-ended (>=) version

• N12: a git or tarball dependency

• N13: dependencies with no lockfile

• N14: an app not marked "private": true

• N15: a file: or link: dependency

What's included

• The scanner (Python 3.9+, standard library only)

• A rules guide with the reason and safer approach for each rule

• A risky and a safe example project, and the real report the scanner produces on the risky one

Limits

It reads your package files as text and does not resolve the dependency tree, so problems inside dependencies are not seen. Lockfiles are checked for presence only. NOT FLAGGED is not a guarantee.

Contents

One ZIP file with 10 files: SKILL.md, the scanner in scripts/ (2 Python files), references/rules.md (every rule with its reason and safer approach), and examples/ (5 example files plus report.md, the real scanner output on the risky example).

How to use: This is an agent skill: a folder with a SKILL.md file and Python scripts that an AI coding agent such as Claude Code, Cursor, or Codex CLI can run. Unzip it into your agent's skills folder (for Claude Code: ~/.claude/skills/), then ask your agent to check your project. The scripts also run on their own with Python 3.9 or newer, with nothing to install. They read your files only: no network access, and nothing is sent anywhere.