execute_javascript

THE RISK

High Risk

Why execute_javascript needs a policy

execute_javascript allows arbitrary JavaScript execution in a browser context, which can modify page state, exfiltrate data, perform financial transactions, or interact with web applications in ways dependent entirely on the JavaScript arguments provided. This is a classic Execute category tool—it runs code whose effects depend on the supplied arguments.

From the tool's definition Tool description states 'Run JavaScript in the active browser tab' with emphasis on execution capability. Server context indicates 'Give AI agents eyes and hands on macOS,' positioning this as an action tool that triggers external operations.

Documented attack patterns abuse exactly the kind of access execute_javascript gives an agent:

POLICY

How to control execute_javascript

PolicyLayer is an MCP gateway — it sits between your AI agents and Macos Control, and nothing reaches the server without passing your rules. This is the rule we recommend for execute_javascript:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "execute_javascript": {
      "limits": [
        {
          "counter": "execute_javascript_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

execute_javascript 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.

Create a free account and register Macos Control — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Macos Control tools

Execute launch_app Open or focus a macOS application by name. Prefer batch_actions when combining with other Execute batch_actions PREFERRED: Always use this tool instead of calling individual action tools (click_at, type Execute click_at Click at x,y screen coordinates. Returns a screenshot by default (disable with return_scre Execute click_by_text Click a button, link, tab, radio, or checkbox by its visible text. Much more reliable than Execute click_element Click a named UI element in an app window. Returns a screenshot by default (disable with r Execute double_click_at Double-click at x,y screen coordinates. Returns a screenshot by default (disable with retu Execute open_url Open a URL in Safari or Chrome. Execute press_key Press a key combo (e.g. press

All 22 Macos Control tools →

Execute tools on other servers

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Go deeper

High-risk tools in Macos Control → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about execute_javascript

What does the execute_javascript tool do? +

Run JavaScript in the active browser tab. Much faster than screenshot+OCR for web pages. Returns the result. It is categorised as a Execute tool in the Macos Control MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on execute_javascript? +

Register the Macos Control MCP server in PolicyLayer and add a rule for execute_javascript: 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 Macos Control. Nothing to install.

What risk level is execute_javascript? +

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

Can I rate-limit execute_javascript? +

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

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

execute_javascript is provided by the Macos Control MCP server (peterhdd/macos-control-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Macos Control tool call.

Start from Macos Control, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →