screenshot · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What screenshot does on Nexus Core

AI agents invoke screenshot to trigger actions in Nexus Core. 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 screenshot needs a policy

This tool both executes a browser action (navigating to an arbitrary URL) and writes a file to the filesystem. Navigation to arbitrary URLs can trigger external requests, load malicious content, or exfiltrate data via URL parameters. The file write adds a Write component, but the external browser execution is the dominant risk, making Execute the appropriate category.

From the tool's definition 'Navigate to URL and write a PNG screenshot to output_path' — performs browser navigation (external operation) and writes a file to disk

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

screenshot Rate-limited

screenshot 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": {
    "screenshot": {
      "limits": [
        {
          "counter": "screenshot_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 Nexus Core, so you can run agents against it safely.

FAQ

Questions about screenshot

What does the screenshot tool do? +

Navigate to URL and write a PNG screenshot to output_path (must be inside ALLOWED_ROOTS). It is categorised as a Execute tool in the Nexus Core MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on screenshot? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for screenshot: 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 Nexus Core. Nothing to install.

What risk level is screenshot? +

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

Can I rate-limit screenshot? +

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

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

screenshot is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.