browserbeam_execute_js · Browserbeam MCP Server MCP

WHAT IT DOES

What browserbeam_execute_js does on Browserbeam MCP Server

AI agents invoke browserbeam_execute_js to trigger actions in Browserbeam MCP Server. 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 browserbeam_execute_js needs a policy

Executing arbitrary JavaScript in a browser context is a code execution capability with unrestricted blast radius. An AI agent could use this to: steal session tokens/cookies, modify DOM and exfiltrate sensitive data, perform unauthorized transactions, redirect users to malicious sites, or trigger any action the authenticated session permits.

From the tool's definition Tool description explicitly states 'Run custom JavaScript in the browser page context'. The incomplete description ('Use') suggests the ability to execute arbitrary code within a live browser session.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browserbeam_execute_js Rate-limited

browserbeam_execute_js 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": {
    "browserbeam_execute_js": {
      "limits": [
        {
          "counter": "browserbeam_execute_js_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 Browserbeam MCP Server, so you can run agents against it safely.

FAQ

Questions about browserbeam_execute_js

What does the browserbeam_execute_js tool do? +

Run custom JavaScript in the browser page context. Use. It is categorised as a Execute tool in the Browserbeam MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on browserbeam_execute_js? +

Register the Browserbeam MCP Server MCP server in PolicyLayer and add a rule for browserbeam_execute_js: 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 Browserbeam MCP Server. Nothing to install.

What risk level is browserbeam_execute_js? +

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

Can I rate-limit browserbeam_execute_js? +

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

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

browserbeam_execute_js is provided by the Browserbeam MCP Server MCP server (nyku/browserbeam-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.