run_js

Server Node Js Sandbox MCP Server ssdeanx/node-code-sandbox-mcp

Category Execute

Risk class High

Parameters 00 required

WHAT IT DOES

What run_js does on Node Js Sandbox MCP Server

AI agents invoke run_js to trigger actions in Node Js Sandbox 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 run_js needs a policy

run_js triggers real processes with real consequences. An agent gone sideways doesn't fire it once — it starts dozens of builds, sends mass notifications, or burns through compute before anyone looks up.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

run_js Rate-limited

run_js 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": {
    "run_js": {
      "limits": [
        {
          "counter": "run_js_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 Node Js Sandbox MCP Server, so you can run agents against it safely.

FAQ

Questions about run_js

What does the run_js tool do? +

Install npm dependencies and run JavaScript code inside a running sandbox container. After running, you must manually stop the sandbox to free resources. The code must be valid ESModules (import/export syntax). Best for complex workflows where you want to reuse the environment across multiple executions. When reading and writing from the Node.js processes, you always need to read from and write to the. It is categorised as a Execute tool in the Node Js Sandbox 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 run_js? +

Register the Node Js Sandbox MCP Server MCP server in PolicyLayer and add a rule for run_js: 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 Node Js Sandbox MCP Server. Nothing to install.

What risk level is run_js? +

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

Can I rate-limit run_js? +

Yes. Add a rate_limit block to the run_js 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 run_js completely? +

Set action: deny in the PolicyLayer policy for run_js. 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 run_js? +

run_js is provided by the Node Js Sandbox MCP Server MCP server (ssdeanx/node-code-sandbox-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.