sms_with_input · Telephony MCP Server MCP: Risk & Policy

WHAT IT DOES

What sms_with_input does on Telephony MCP Server

AI agents use sms_with_input 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 sms_with_input needs a policy

This tool sends SMS messages to real-world phone numbers via the Vonage API. Sending an SMS is a Write operation (creates and delivers a message) with real-world side effects. Severity is high because an AI agent could send unsolicited or malicious SMS messages to arbitrary phone numbers at scale, potentially constituting harassment or spam.

From the tool's definition Send an SMS to a recipient and wait for an event... Uses the Vonage SMS API

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

sms_with_input Rate-limited

sms_with_input 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": {
    "sms_with_input": {
      "limits": [
        {
          "counter": "sms_with_input_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 sms_with_input

What does the sms_with_input tool do? +

Send an SMS to a recipient and wait for an event at {CALLBACK_SERVER_URL}/event. When an event arrives for the same msisdn, display the text and stop waiting. Uses 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 sms_with_input? +

Register the Telephony MCP Server MCP server in PolicyLayer and add a rule for sms_with_input: 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 sms_with_input? +

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

Can I rate-limit sms_with_input? +

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

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

sms_with_input 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.