evaluate_js_on_element · InSite MCP: Risk & Policy

WHAT IT DOES

What evaluate_js_on_element does on InSite

AI agents invoke evaluate_js_on_element to trigger actions in InSite. 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 evaluate_js_on_element needs a policy

This tool allows running arbitrary JavaScript in the browser context, which can perform any operation accessible from JavaScript (DOM manipulation, cookie access, network requests, form submission, etc.). While technically confined to a specific element, JavaScript execution at element scope can still access global context and perform side effects.

From the tool's definition Tool name 'evaluate_js_on_element' and description 'Execute JavaScript code on a specific element' explicitly indicate execution of arbitrary JavaScript code.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

evaluate_js_on_element Rate-limited

evaluate_js_on_element 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": {
    "evaluate_js_on_element": {
      "limits": [
        {
          "counter": "evaluate_js_on_element_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 InSite, so you can run agents against it safely.

FAQ

Questions about evaluate_js_on_element

What does the evaluate_js_on_element tool do? +

Execute JavaScript code on a specific element. It is categorised as a Execute tool in the InSite MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on evaluate_js_on_element? +

Register the InSite MCP server in PolicyLayer and add a rule for evaluate_js_on_element: 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 InSite. Nothing to install.

What risk level is evaluate_js_on_element? +

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

Can I rate-limit evaluate_js_on_element? +

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

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

evaluate_js_on_element is provided by the InSite MCP server (jowharshamshiri/insite). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.