browser_emulate_device · Byob MCP: Risk & Policy

WHAT IT DOES

What browser_emulate_device does on Byob

AI agents invoke browser_emulate_device to trigger actions in Byob. 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 browser_emulate_device needs a policy

This tool triggers a browser state change (device viewport emulation) whose effects depend on arguments (device type, screen size, user agent, etc.). It is an external operation executed against a running Chrome instance. While not destructive or financial, and beyond simple data retrieval, it modifies the browser environment and could affect subsequent actions or data collection.

From the tool's definition Tool description states 'Emulate a device viewport' and is part of a server that 'Lets AI assistants control your real Chrome browser' with capabilities including 'clicking, and typing'.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_emulate_device Rate-limited

browser_emulate_device 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": {
    "browser_emulate_device": {
      "limits": [
        {
          "counter": "browser_emulate_device_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 Byob, so you can run agents against it safely.

FAQ

Questions about browser_emulate_device

What does the browser_emulate_device tool do? +

Emulate a device viewport. Use. It is categorised as a Execute tool in the Byob MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on browser_emulate_device? +

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

What risk level is browser_emulate_device? +

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

Can I rate-limit browser_emulate_device? +

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

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

browser_emulate_device is provided by the Byob MCP server (wxtsky/byob). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.