Guides

Package guard

Check packages before an agent installs them — hallucinated names, malicious packages, known vulnerabilities and typosquats — via MCP, REST or a Claude Code hook.

Coding agents sometimes invent package names. Attackers watch for those names and register them ("slopsquatting"), so the next agent that hallucinates the same name installs malware. The package guard checks every package before it is installed.

What is checked

Check	Source	Verdict
The package exists in the registry	deps.dev, then the registry itself for brand-new packages	missing → block
The requested version was published	deps.dev / registry	missing → block
Malicious-package report (`MAL-…`)	OSV	block
Known vulnerabilities in that version, with the fixed version	OSV (GHSA, PyPA, Go, RustSec…)	warn
Deprecated or yanked	deps.dev / crates.io	warn
First published less than 30 days ago	deps.dev / registry	warn
Fewer than 500 downloads last week (npm)	api.npmjs.org	warn
Name one or two edits away from a popular package (`expres`, `reqeusts`)	CodexGuild list	warn

block means do not install. warn means tell the user why before installing. ok means nothing was found. unknown means a lookup failed. The guard never blocks because of an outage.

Ecosystems: npm, pypi, go, cargo. Only names and versions are sent.

MCP

text

codexguild_check_packages { packages: [{ name: "zod", ecosystem: "npm", version: "^3.25.0" }] }

REST

bash

curl -s -X POST https://api.codexguild.com/v1/packages/check \
  -H "Authorization: Bearer $CODEXGUILD_API_KEY" -H "content-type: application/json" \
  -d '{"packages":[{"name":"reqeusts","ecosystem":"pypi"},{"name":"lodash","ecosystem":"npm","version":"4.17.15"}]}'

Claude Code hook (automatic)

The local MCP package also contains a PreToolUse hook. It reads each Bash command before it runs and finds installs:

npm / pnpm / yarn / bun add
npx, bunx, pnpm dlx
pip install, uv add, uvx, poetry add, pipx
cargo add
go get

If a package is blocked, the hook denies the command and tells the agent why. If a package gets a warning, Claude Code asks you before the command runs. Lockfile installs (npm ci, npm install with no arguments) and local paths are never checked.

Add it to ~/.claude/settings.json (or the project's .claude/settings.json):

json

{
  "env": { "CODEXGUILD_API_KEY": "cgk_..." },
  "hooks": {
    "PreToolUse": [
      { "matcher": "Bash", "hooks": [{ "type": "command", "command": "npx -y @codexguild/mcp@latest guard", "timeout": 20 }] }
    ]
  }
}

If the key is missing or CodexGuild can't be reached, the hook lets the command run and prints a note.