browser.start_session · MCP Fullstack MCP: Risk & Policy

WHAT IT DOES

What browser.start_session does on MCP Fullstack

AI agents invoke browser.start_session to trigger actions in MCP Fullstack. 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.start_session needs a policy

This tool initiates a browser automation session, which is an Execute action—it triggers external operations (browser control) whose side effects are determined by subsequent commands. While the session start itself is not directly destructive or financial, it is the gateway to executing browser automation workflows that could modify state, extract data, or trigger unintended side effects.

From the tool's definition Tool name is 'browser.start_session' and description states 'Start a new browser session'. Per server description, this platform provides 'browser automation' capabilities.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser.start_session Rate-limited

browser.start_session 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.start_session": {
      "limits": [
        {
          "counter": "browser.start_session_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 MCP Fullstack, so you can run agents against it safely.

FAQ

Questions about browser.start_session

What does the browser.start_session tool do? +

Start a new browser session. It is categorised as a Execute tool in the MCP Fullstack 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.start_session? +

Register the MCP Fullstack MCP server in PolicyLayer and add a rule for browser.start_session: 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 MCP Fullstack. Nothing to install.

What risk level is browser.start_session? +

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

Can I rate-limit browser.start_session? +

Yes. Add a rate_limit block to the browser.start_session 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.start_session completely? +

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

browser.start_session is provided by the MCP Fullstack MCP server (jacobfv/mcp-fullstack). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.