evaluate · Chromium ARM64 Browser MCP: Risk & Policy

WHAT IT DOES

What evaluate does on Chromium ARM64 Browser

AI agents invoke evaluate to trigger actions in Chromium ARM64 Browser. 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 needs a policy

Although the description claims 'read-only operations,' the tool fundamentally executes JavaScript in the browser context. JavaScript execution is inherently in the Execute category because it can trigger side effects (network requests, DOM manipulation, storage access, event firing) and may escape read-only constraints through creative scripting.

From the tool's definition Tool description states "Execute JavaScript in the browser" — JavaScript execution is a form of code execution that can trigger arbitrary operations depending on the script content, even if nominally labeled "read-only."

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

evaluate Rate-limited

evaluate 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": {
      "limits": [
        {
          "counter": "evaluate_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 Chromium ARM64 Browser, so you can run agents against it safely.

FAQ

Questions about evaluate

What does the evaluate tool do? +

Execute JavaScript in the browser (read-only operations). It is categorised as a Execute tool in the Chromium ARM64 Browser 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? +

Register the Chromium ARM64 Browser MCP server in PolicyLayer and add a rule for evaluate: 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 Chromium ARM64 Browser. Nothing to install.

What risk level is evaluate? +

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

Can I rate-limit evaluate? +

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

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

evaluate is provided by the Chromium ARM64 Browser MCP server (nfodor/mcp-chromium-arm64). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.