cast_resume · Kef MCP: Risk & Policy

WHAT IT DOES

What cast_resume does on Kef

AI agents invoke cast_resume 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 cast_resume needs a policy

This tool triggers an external operation on a physical device (KEF speaker) — resuming Cast playback. It has a real-world side effect (audio starts playing) but is reversible and low-blast-radius. It fits Execute as it triggers an external operation rather than simply reading or writing data.

From the tool's definition Resume paused Cast playback on the KEF

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

cast_resume Rate-limited

cast_resume 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": {
    "cast_resume": {
      "limits": [
        {
          "counter": "cast_resume_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 cast_resume

What does the cast_resume tool do? +

Resume paused Cast playback on the KEF. 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 cast_resume? +

Register the Kef MCP server in PolicyLayer and add a rule for cast_resume: 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 cast_resume? +

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

Can I rate-limit cast_resume? +

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

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

cast_resume 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.