calls_end · Slack MCP: Risk & Policy

WHAT IT DOES

What calls_end does on Slack

AI agents invoke calls_end to trigger actions in Slack. 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 calls_end needs a policy

Ending a call is an irreversible action for that call session (you cannot 'un-end' a call), but it doesn't delete data or move money. It triggers an external operation (terminating a live call) whose impact depends on context — could disrupt active meetings. Closest to Execute since it triggers an external operation, though it has a mild destructive flavor. Severity is medium as it can disrupt ongoing communications.

From the tool's definition 'End a call' — terminates an active Slack call session, which is an external operation with real effects on ongoing communications

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

calls_end Rate-limited

calls_end 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": {
    "calls_end": {
      "limits": [
        {
          "counter": "calls_end_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

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PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Slack, so you can run agents against it safely.

FAQ

Questions about calls_end

What does the calls_end tool do? +

End a call. It is categorised as a Execute tool in the Slack MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on calls_end? +

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

What risk level is calls_end? +

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

Can I rate-limit calls_end? +

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

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

calls_end is provided by the Slack MCP server (karbassi/slack-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.