create_call · Vapi MCP Server MCP: Risk & Policy

WHAT IT DOES

What create_call does on Vapi MCP Server

AI agents invoke create_call to trigger actions in Vapi MCP 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 create_call needs a policy

Initiating an outbound phone call is an external operation with real-world consequences: it contacts real phone numbers, consumes telephony resources, and engages recipients. While not directly financial or destructive, it executes an action in the external world that cannot simply be undone once the call is placed.

From the tool's definition Creates an outbound call — triggers an external real-world phone call operation whose effects (dialing a phone number, connecting a voice AI assistant) are immediate and depend on the arguments provided.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_call Rate-limited

create_call 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": {
    "create_call": {
      "limits": [
        {
          "counter": "create_call_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 Vapi MCP Server, so you can run agents against it safely.

FAQ

Questions about create_call

What does the create_call tool do? +

Creates a outbound call. It is categorised as a Execute tool in the Vapi MCP 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 create_call? +

Register the Vapi MCP Server MCP server in PolicyLayer and add a rule for create_call: 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 Vapi MCP Server. Nothing to install.

What risk level is create_call? +

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

Can I rate-limit create_call? +

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

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

create_call is provided by the Vapi MCP Server MCP server (kuchikirenji/mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.