I Built a Claude Code Plugin That Blocks Hallucinated Package Versions

The Problem

If you use Claude Code (Anthropic's CLI coding agent), you've probably seen it do things like:

npm install lodash@4.17.21

...when the latest version is actually different, or worse — install a version that doesn't even exist on the registry. Claude hallucinates package versions just like it hallucinates everything else.

This is a supply-chain risk. You end up with outdated deps, missing security patches, or broken installs.

The Solution: Version Sentinel

I built Version Sentinel — a Claude Code plugin that uses the hook system to hard-block any dependency change until you've verified the version is real and current.

How it works

1. PreToolUse hooks intercept edits to manifest files (package.json, requirements.txt, pyproject.toml, Cargo.toml, *.csproj) and install commands (npm install, pip install, cargo add, dotnet add)
2. If no fresh version check exists → action is blocked (exit code 2)
3. You run WebSearch to verify the latest version, then /vs-record to log it
4. Claude retries and the action goes through
5. PostToolUse hooks auto-record successful installs so verified packages stay unblocked

Supported ecosystems

Ecosystem	Manifest	Registry
npm	package.json	registry.npmjs.org
pip	requirements*.txt, pyproject.toml	pypi.org
Cargo	Cargo.toml	crates.io
.NET	*.csproj	api.nuget.org

Bonus: /check-versions

Audits ALL dependencies in your project against upstream registries. Reports drift without blocking — shows you which deps are outdated and which are intentionally pinned.

Install

claude plugin add KSEGIT/Version-Sentinel

Links

• GitHub: KSEGIT/Version-Sentinel
• License: MIT
• Prerequisites: bash, jq, curl, python3

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This is my first Claude Code plugin. Would love feedback — especially if you've run into the same version hallucination problem. What other guardrails would be useful?