stop_playback · MCP Media Server MCP: Risk & Policy

WHAT IT DOES

What stop_playback does on MCP Media Server

AI agents invoke stop_playback to trigger actions in MCP Media Server. 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 executes a command that controls an external application (MPV media player). While the action is reversible (the user can simply restart playback), it qualifies as Execute rather than Write because it directly triggers a process termination rather than modifying stored data. Severity is low because the impact is limited to stopping media playback with no data loss, financial impact, or system compromise.

From the tool's definition The tool description states it will 'Stop playback and quit MPV' — this triggers an external operation (terminating the media player process) whose effects depend on the current system state.

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 MCP Media Server, so you can run agents against it safely.

FAQ

Questions about stop_playback

What does the stop_playback tool do? +

Stop playback and quit MPV. It is categorised as a Execute tool in the MCP Media Server 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 MCP Media Server 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 MCP Media Server. 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 MCP Media Server MCP server (neal3000/mcp_media_server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.