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.
This tool sends SMS messages, which is a write operation—it creates new outbound communication. While the sent message cannot be recalled, this is classified as Write rather than Execute or Destructive because: (1) it modifies state by creating a message transmission rather than executing arbitrary code, (2) it has a clear, bounded effect (sending a single SMS), and (3) there is no capability to delete or…
From the tool's definition The tool 'send_sms' uses the Vonage SMS API to send SMS messages, as stated in the description. This is a write operation that creates/sends communication but is reversible in the sense that the action itself cannot be undone but is not destructive of data or…
Documented attack patterns abuse exactly the kind of access send_sms gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Telephony MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for send_sms:
{
"version": "1",
"default": "deny",
"tools": {
"send_sms": {
"limits": [
{
"counter": "send_sms_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}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.
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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.
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.
send_sms is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
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.
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.
send_sms is provided by the Telephony MCP Server MCP server (khan2a/telephony-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Telephony MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
5 Telephony MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.