browser_close_tab · Byob MCP: Risk & Policy

WHAT IT DOES

What browser_close_tab does on Byob

AI agents use browser_close_tab to create or update resources in Byob — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Byob environment.

WHY IT NEEDS A POLICY

Why browser_close_tab needs a policy

An AI agent can call browser_close_tab faster than any human can review — one bad instruction and it creates or modifies resources in Byob by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_close_tab Rate-limited

browser_close_tab stays usable, but capped — an agent stuck in a loop can't make hundreds of changes 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_close_tab": {
      "limits": [
        {
          "counter": "browser_close_tab_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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_close_tab

What does the browser_close_tab tool do? +

Close a browser tab by tabId. Returns tab_closed if the tab does not exist. It is categorised as a Write tool in the Byob MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on browser_close_tab? +

Register the Byob MCP server in PolicyLayer and add a rule for browser_close_tab: 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_close_tab? +

browser_close_tab is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit browser_close_tab? +

Yes. Add a rate_limit block to the browser_close_tab 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_close_tab completely? +

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

browser_close_tab 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.