set_representation · Vmd MCP: Risk & Policy

WHAT IT DOES

What set_representation does on Vmd

AI agents use set_representation 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 set_representation needs a policy

set_representation creates or modifies visual representations in VMD2 without deleting underlying data or executing arbitrary code. The change is reversible (another representation can be set), making it Write rather than Destructive. While it operates in a scientific visualization context, the core action is data modification.

From the tool's definition Tool description states 'Replace all visual representations of a molecule with a single new one' — this modifies the visual state of loaded molecular structures. It is a reversible change to representation parameters.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_representation Rate-limited

set_representation 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_representation": {
      "limits": [
        {
          "counter": "set_representation_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 set_representation

What does the set_representation tool do? +

Replace all visual representations of a molecule with a single new one. 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 set_representation? +

Register the Vmd MCP server in PolicyLayer and add a rule for set_representation: 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 set_representation? +

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

Can I rate-limit set_representation? +

Yes. Add a rate_limit block to the set_representation 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_representation completely? +

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

set_representation 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.