send_sms · Telephony MCP Server MCP: Risk & Policy

WHAT IT DOES

What send_sms does on Telephony MCP Server

AI agents use send_sms to create or update resources in Telephony MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Telephony MCP Server environment.

WHY IT NEEDS A POLICY

Why send_sms needs a policy

Sending an SMS creates an outbound message via an external API, which is a write/create action with real-world side effects. It cannot be trivially undone once sent. Severity is high because a misused agent could send spam, phishing messages, or harass recipients at scale using the Vonage API, potentially incurring costs and legal liability.

From the tool's definition Send an SMS using the Vonage SMS API

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_sms Rate-limited

send_sms stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "send_sms": {
      "limits": [
        {
          "counter": "send_sms_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about send_sms

What does the send_sms tool do? +

Send an SMS using the Vonage SMS API. It is categorised as a Write tool in the Telephony MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on send_sms? +

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

What risk level is send_sms? +

send_sms is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit send_sms? +

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

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

send_sms is provided by the Telephony MCP Server MCP server (vonage-community/telephony-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.