set_viewport · JS Reverse MCP: Risk & Policy

WHAT IT DOES

What set_viewport does on JS Reverse MCP

AI agents use set_viewport to create or update resources in JS Reverse MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your JS Reverse MCP environment.

WHY IT NEEDS A POLICY

Why set_viewport needs a policy

This tool modifies the browser viewport configuration, which is a reversible write operation affecting the display dimensions of the active page. It has minimal blast radius as it only changes rendering parameters and does not execute code, access sensitive data, or perform destructive actions.

From the tool's definition Set the active page viewport size

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_viewport Rate-limited

set_viewport stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_viewport": {
      "limits": [
        {
          "counter": "set_viewport_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches JS Reverse MCP, so you can run agents against it safely.

FAQ

Questions about set_viewport

What does the set_viewport tool do? +

Set the active page viewport size. It is categorised as a Write tool in the JS Reverse MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_viewport? +

Register the JS Reverse MCP server in PolicyLayer and add a rule for set_viewport: 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 JS Reverse MCP. Nothing to install.

What risk level is set_viewport? +

set_viewport is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit set_viewport? +

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

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

set_viewport is provided by the JS Reverse MCP server (noone-hub/jsreverser-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.