open_url

THE RISK

High Risk

Why open_url needs a policy

Opening a URL causes a browser to navigate to an external resource, which is an external operation with side effects (network requests, potential downloads, page execution). It is not a simple read/query of local data, but an action that drives the browser — classified as Execute. Misuse could lead to navigating to malicious pages, triggering downloads, or other browser-based attacks.

From the tool's definition Open a URL in Safari or Chrome — triggers an external browser operation

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

POLICY

How to control open_url

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 open_url:

policy.json

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

open_url 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

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All 22 Macos Control tools →

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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 open_url

What does the open_url tool do? +

Open a URL in Safari or Chrome. 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 open_url? +

Register the Macos Control MCP server in PolicyLayer and add a rule for open_url: 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 open_url? +

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

Can I rate-limit open_url? +

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

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

open_url 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 →