render_image · Vmd MCP: Risk & Policy

WHAT IT DOES

What render_image does on Vmd

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

WHY IT NEEDS A POLICY

Why render_image needs a policy

This tool creates a new image file on disk by rendering the current VMD viewport. It writes data (an image file) to the filesystem, which is a reversible write operation (the file can be deleted). It does not execute arbitrary code, delete data, or involve financial transactions. Severity is medium because it writes files to the filesystem, potentially overwriting existing files without warning.

From the tool's definition Render the current VMD viewport to an image file

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

render_image Rate-limited

render_image 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": {
    "render_image": {
      "limits": [
        {
          "counter": "render_image_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 Vmd, so you can run agents against it safely.

FAQ

Questions about render_image

What does the render_image tool do? +

Render the current VMD viewport to an image file. It is categorised as a Write tool in the Vmd MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on render_image? +

Register the Vmd MCP server in PolicyLayer and add a rule for render_image: 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 Vmd. Nothing to install.

What risk level is render_image? +

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

Can I rate-limit render_image? +

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

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

render_image is provided by the Vmd MCP server (omararias-gaguancela/vmd-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.