play_radio · Kef MCP: Risk & Policy

WHAT IT DOES

What play_radio does on Kef

AI agents invoke play_radio to trigger actions in Kef. 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 play_radio needs a policy

This tool initiates an external operation (casting a stream URL to a physical KEF speaker device). It is not a simple data read or write; it executes a Cast command that causes real-world effects on hardware. No financial or irreversible destructive action is involved.

From the tool's definition 'Play internet radio / a direct stream URL on the KEF via Google Cast' — triggers external playback operation on a physical device via Google Cast

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

play_radio Rate-limited

play_radio 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": {
    "play_radio": {
      "limits": [
        {
          "counter": "play_radio_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 Kef, so you can run agents against it safely.

FAQ

Questions about play_radio

What does the play_radio tool do? +

Play internet radio / a direct stream URL on the KEF via Google Cast. It is categorised as a Execute tool in the Kef MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on play_radio? +

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

What risk level is play_radio? +

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

Can I rate-limit play_radio? +

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

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

play_radio is provided by the Kef MCP server (nqrwhal/kef-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.