browser_session_start · Wmux MCP: Risk & Policy

WHAT IT DOES

What browser_session_start does on Wmux

AI agents invoke browser_session_start to trigger actions in Wmux. 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_session_start needs a policy

Starting a browser session is an Execute-class action: it runs an external process (a browser) whose behavior and side effects depend on the profile argument and subsequent browser operations. While not immediately destructive or financial, an uncontrolled browser session could be used for unauthorized access, credential theft, or malicious web interactions.

From the tool's definition Tool name 'browser_session_start' and description 'Start a browser session with the specified profile' indicate the tool initiates a browser session, which is an external operation that executes in a real browser environment.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_session_start Rate-limited

browser_session_start 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_session_start": {
      "limits": [
        {
          "counter": "browser_session_start_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 Wmux, so you can run agents against it safely.

FAQ

Questions about browser_session_start

What does the browser_session_start tool do? +

Start a browser session with the specified profile. It is categorised as a Execute tool in the Wmux 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_session_start? +

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

What risk level is browser_session_start? +

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

Can I rate-limit browser_session_start? +

Yes. Add a rate_limit block to the browser_session_start 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_session_start completely? +

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

browser_session_start is provided by the Wmux MCP server (openwong2kim/wmux). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.