stop_playback · Vmd MCP: Risk & Policy

WHAT IT DOES

What stop_playback does on Vmd

AI agents invoke stop_playback to trigger actions in Vmd. 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 stop_playback needs a policy

This tool triggers an external operation (stopping VMD's animation playback) whose effects depend on the current state of the application. While not destructive or creating side effects on data, it executes a control action in VMD. The severity is medium because misuse would interrupt user workflows but causes no permanent data loss or financial impact.

From the tool's definition Tool name 'stop_playback' and description 'Stop any currently running trajectory animation in VMD' indicates execution of a control command that halts an active process in the VMD molecular dynamics software.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

stop_playback Rate-limited

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

FAQ

Questions about stop_playback

What does the stop_playback tool do? +

Stop any currently running trajectory animation in VMD. It is categorised as a Execute tool in the Vmd MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on stop_playback? +

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

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

Can I rate-limit stop_playback? +

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

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

stop_playback 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.