npm_run · NVM MCP Server MCP: Risk & Policy

WHAT IT DOES

What npm_run does on NVM MCP Server

AI agents invoke npm_run to trigger actions in NVM MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why npm_run needs a policy

This tool allows execution of npm commands, which can run arbitrary JavaScript code through npm scripts, install dependencies with pre/post-install hooks that execute code, and trigger other side effects. The effects depend on the arguments passed (which npm command, which script, what package.json exists).

From the tool's definition Tool description states it 'Run[s] the `npm` binary' with a specified Node version. npm is a package manager that executes arbitrary scripts defined in package.json files (via 'npm run' commands, install hooks, lifecycle scripts, etc.).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

npm_run Rate-limited

npm_run stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "npm_run": {
      "limits": [
        {
          "counter": "npm_run_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches NVM MCP Server, so you can run agents against it safely.

FAQ

Questions about npm_run

What does the npm_run tool do? +

Run the npm binary with the session-active (or a specified) NVM version. It is categorised as a Execute tool in the NVM MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on npm_run? +

Register the NVM MCP Server MCP server in PolicyLayer and add a rule for npm_run: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches NVM MCP Server. Nothing to install.

What risk level is npm_run? +

npm_run is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit npm_run? +

Yes. Add a rate_limit block to the npm_run rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block npm_run completely? +

Set action: deny in the PolicyLayer policy for npm_run. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides npm_run? +

npm_run is provided by the NVM MCP Server MCP server (realjacoblinder/nvm-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.